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“Fortunately for me the symptoms so far have been very mild so I’ve been able to carry on with the work driving forward the UK response,” he said. “I’ll be continuing to do everything I can to get our carers the support that they need. And I’ll be doing that from here but with no less gusto.”

A Downing Street spokeswoman said: “After experiencing mild symptoms yesterday, the prime minister was tested for coronavirus on the personal advice of England’s chief medical officer, Prof Chris Whitty. The test was carried out in No 10 by NHS staff and the result of the test was positive.

Earlier in the week it was announced that the Prince of Wales had “mild symptoms” of the disease. The Labour MP Angela Rayner, the favourite to become the party’s deputy leader, announced on Twitter that she was self-isolating after displaying symptoms.

Ian Blackford, the Scottish National party’s leader in the House of Commons, said the news showed no one was immune.

Johnson posted a video on Friday morning on Twitter saying he had a temperature and a persistent cough. “I am working from home, I’m self-isolating, and that’s entirely the right thing to do,” he said.

After the prime minister, who is 55, said he had mild symptoms and would self-isolate in Downing Street, Hancock posted a Twitter video saying that he too had mild symptoms and he would be able to continue.

Boris Johnson and health secretary Matt Hancock have both tested positive for coronavirus and will have to work leading the government’s efforts to tackle the pandemic in isolation.

“Fortunately for me the symptoms so far have been very mild so I’ve been able to carry on with the work driving forward the UK response,” he said. “I’ll be continuing to do everything I can to get our carers the support that they need. And I’ll be doing that from here but with no less gusto.”

The World Health Organization has said there is no evidence that pregnant women are at higher risk of severe illness than the general population if they contract Covid-19.

Earlier in the week it was announced that the Prince of Wales had “mild symptoms” of the disease. The Labour MP Angela Rayner, the favourite to become the party’s deputy leader, announced on Twitter that she was self-isolating after displaying symptoms.

journalism that is rooted in empirical data and science matters. It may even save lives. This administration has cleared out science and scientists across all departments. Donald Trump's daily coronavirus press briefings have become political rallies. He frequently spreads, at best, misinformation and, at worst, lies.

Federal health officials also offered two new ways to shorten quarantine periods. Those without symptoms may end quarantine after seven days if they are tested for the virus and receive a negative result, or after 10 days without a negative test.

“We are at the point now, even before Christmas, that there may not be room at your hospital, because we don’t have enough health care workers to take care of you,”

Until now, the C.D.C. has recommended a 14-day quarantine period following potential exposure, and Dr. Walke stressed that the full two weeks is still considered ideal and the surest way to curb transmissions.

Daily deaths have been exceeding 2,000 for the first time since early May, and close to 100,000 Americans are already hospitalized.

Some patients may not develop symptoms until two weeks after exposure, and even longer in a very small fraction of cases. Infected individuals may pass the virus to others before they develop symptoms; recent studies show they are most infectious two days before symptoms begin, and for about five days afterward.

Federal health officials also offered two new ways to shorten quarantine periods. Those without symptoms may end quarantine after seven days if they are tested for the virus and receive a negative result, or after 10 days without a negative test.

“We can safely reduce the length of quarantine, but accepting that there is a small residual risk that a person who is leaving quarantine early could transmit to someone else if they became infected,”

Some patients may not develop symptoms until two weeks after exposure, and even longer in a very small fraction of cases. Infected individuals may pass the virus to others before they develop symptoms; recent studies show they are most infectious two days before symptoms begin, and for about five days afterward.

Indeed, doctors are reporting similar cases across the country and around the world. A small number of Covid patients who had never experienced mental health problems are developing severe psychotic symptoms weeks after contracting the coronavirus

Beyond individual reports, a British study of neurological or psychiatric complications in 153 patients hospitalized with Covid-19 found that 10 people had “new-onset psychosis.”

Although the coronavirus was initially thought primarily to cause respiratory distress, there is now ample evidence of many other symptoms, including neurological, cognitive and psychological effects, that could emerge even in patients who didn’t develop serious lung, heart or circulatory problems.

Medical experts say they expect that such extreme psychiatric dysfunction will affect only a small proportion of patients. But the cases are considered examples of another way the Covid-19 disease process can affect mental health and brain function.

Experts increasingly believe brain-related effects may be linked to the body’s immune system response to the coronavirus and possibly to vascular problems or surges of inflammation caused by the disease process.

Also striking is that most patients have been in their 30s, 40s and 50s. “It’s very rare for you to develop this type of psychosis in this age range,”

Some post-Covid patients who developed psychosis needed weeks of hospitalization in which doctors tried different medications before finding one that helped.

Persistent immune activation is also a leading explanation for brain fog and memory problems bedeviling many Covid survivors,

How long the psychosis lasted and patients’ response to treatment has varied. The woman in Britain — whose symptoms included paranoia about the color red and terror that nurses were devils who would harm her and a family member — took about 40 days to recover, according to a case report.

By the time she felt mostly better, it was mid-May, although some of her symptoms still routinely re-emerge, she says.

“To me, and I think most people, the definition of ‘mild’, passed down from the WHO and other authorities, meant any case that didn’t require hospitalization at all, that anyone who wasn’t hospitalized was just going to have a small cold and could take care of it at home,”

“From my point of view, this has been a really harmful narrative and absolutely has misinformed the public. It both prohibits people from taking relevant information into account when deciding their personal risk levels, and it prevents the long-haulers from getting the help they need.”

One of the first questions experts asked me was whether my family was vaccinated. Yes, I said: My husband and I are vaccinated and boosted, and our kids are vaccinated but not yet boosted. This is a relevant question because, if you’re exposed to the virus that causes Covid-19, “your immune system kicks into action a lot faster if you’re vaccinated versus not vaccinated,”

First, the swift immune reaction slows the rate of viral reproduction and spread. “This is what the vaccines are there for — to educate your immune system so that it gets a jump on the invaders before they are able to replicate out of control,”

Because the virus doesn’t replicate as quickly in vaccinated people, they may be less likely to test positive for Covid-19 after coronavirus exposure, because their immune system “keeps the viral load below the level of detection,”

It’s possible, then, that my husband and son did catch Covid-19, but their vaccinated immune systems fended off the infection so well that they never had enough viral proteins in their nose or throat to test positive. And their continual negative tests probably meant that they were never that contagious

If my husband and son never tested positive, why did they feel sick? Even if a vaccinated person doesn’t have much virus in their body, they can still have powerful Covid symptoms

That’s because many illness symptoms — fever, malaise, runny nose, fatigue — are actually caused by the immune system’s response to the virus, rather than the virus itself

And as for why I felt fine, Dr. Morrison said that perhaps my immune system fought off the incoming virus so quickly that I didn’t even have a chance to feel sick. “It sounds to me like you were definitely exposed,”

maybe I had high levels of vaccine antibodies or immune cells called T cells that were able to kill the invading virus before it had a chance to alert the parts of my immune system that would incite symptoms.

All this said, nobody really knows what happened to me, my son or my husband. When it comes to understanding how Covid-19 affects the body, “there are so many open questions,”

people can have different experiences for many different reasons. For instance, Dr. Andino said, it’s possible that the virus was replicating in parts of my husband’s or my son’s body that the tests didn’t reach

Research suggests that the coronavirus can replicate in the pancreas, heart, brain, kidneys and other organs, although vaccination may reduce the chance that the virus spreads outside the respiratory system.

Dr. Andino said that he and his colleagues have been conducting studies in which they follow and repeatedly test entire households after one person in the home tests positive for Covid-19. “What we see is exactly what you described — that some people in the household don’t test positive,”

if healthy individuals start stockpiling surgical masks and high-grade N95 masks, they can also make it harder for health workers to get the resources they need to help on the front lines.

But studies of influenza pandemics have shown that when high-grade N95 masks are not available, surgical masks do protect people a bit more than not wearing masks at all. And when masks are combined with hand hygiene, they help reduce the transmission of infections.

When researchers conducted systematic review of a variety of interventions used during the SARS outbreak in 2003, they found that washing hands more than 10 times daily was 55 percent effective in stopping virus transmission, while wearing a mask was actually more effective — at about 68 percent

Wearing gloves offered about the same amount of protection as frequent hand-washing, and combining all measures — hand-washing, masks, gloves and a protective gown — increased the intervention effectiveness to 91 percent.

Classified data from the Chinese government that was reported in the South China Morning Post indicated that up to a third of all people who tested positive for the coronavirus could have been silent carriers.

Widespread testing on the Diamond Princess showed that half of the positive cases on board the cruise ship had no symptoms.

While wearing a mask may not necessarily prevent healthy people from getting sick, and it certainly doesn’t replace important measures such as hand-washing or social distancing, it may be better than nothing,

“It’s still hard to tell what percentage of people are truly asymptomatic because many go on to develop symptoms a few days later,

“What we do know is that individuals can shed virus about 48 hours before they develop symptoms and masking can prevent transmission from those individuals.”

Wearing a mask can also reduce the likelihood that people will touch their face

In many Asian countries, everyone is encouraged to wear masks, and the approach is about crowd psychology and protection. If everyone wears a mask, individuals protect each other, reducing overall community transmission

The sick automatically have one on and are also more likely to adhere to keeping their mask on because the stigma of wearing one is removed.

Masks are also an important signal that it’s not business as usual during a pandemic

They may also serve as an act of solidarity, showing that all citizens are on board with the precautionary measures needed to bring infections under control.

“If everyone in the community wears a mask, it could decrease transmission,” Dr. Fishman said. “But unfortunately I think that we don’t have enough masks to make that effective policy in the U.S.”

This month, a study that analyzed electronic medical records in California found that nearly a third of the people struggling with long Covid symptoms — like shortness of breath, cough and abdominal pain — did not have any signs of illness in the first 10 days after they tested positive for the coronavirus. Surveys by patient-led groups have also found that many Covid survivors with long-term symptoms were never hospitalized for the disease.

Participants in the study were overwhelmingly white, and 70 percent were women. Dr. Navis and others said that the lack of diversity quite likely reflected the demographics of people able to seek care relatively early in the pandemic rather than the full spectrum of people affected by post-Covid neurological sympto

In the Northwestern study, 43 percent of the patients had depression before having Covid-19; 16 percent had previous autoimmune diseases, the same percentage of patients who had previous lung disease or had struggled with insomnia.

“Waking up every day in this body, sometimes hope feels a little dangerous,” said Ms. Khan, who will soon start the cognitive rehab program. “I have to wonder: Am I going to recover, or am I going to just figure out how to live with my new brain?”

ost scientists say that people who have had Covid-19 gain some immunity to the virus that causes it. What they don’t know is whether that protection lasts a few months, a few years or a lifetime.

The immune system wards off infections by producing antibodies that fight invaders. A range of hereditary and environmental factors, including diet and sleep patterns, typically affect the strength and longevity of those defenses.

Immunity also depends on the pathogen. For example, infection by the virus that causes measles confers lifelong immunity. Others, like the influenza virus, can mutate so rapidly that protective antibodies might not recognize them during a reinfection.

The novel coronavirus mutates more slowly than the influenza virus. That gives researchers hope that any natural immunity, or vaccine, would offer more lasting protection. Even if someone gets sick again, researchers believe a second infection might be milder than the first.

Data are scant, but preliminary research shows antibodies can emerge within days or several weeks of the onset of symptoms. A study involving 34 hospitalized cases in China found that two patients, both in their 80s, produced antibodies within three days of symptom onset. The rest produced them two weeks after symptoms first surfaced.

A group of Chinese researchers reported in March that they had infected four rhesus macaques, allowed them to recover and then tried to reinfect two of them with the same strain of the virus. Neither became sick again.

Then why are some people testing positive again? South Korean health officials are refraining from labeling them as “reinfections.” Korean doctors involved in a continuing government review believe that those patients likely harbored low levels of the virus that diagnostic polymerase chain reaction, or PCR, tests failed to pick up. In later stages of the disease, the virus settles into the lungs where it can elude detection. The virus, they say, hadn’t been fully cleared from the body.

ow do I know I’ve fully recovered? Clinicians have mixed views on what constitutes recovery because long-term data aren’t yet available. Guidelines vary across the globe, and even within countries. In a peer-reviewed study published last month, researchers in Hong Kong detected the virus in the feces of Covid-19 survivors even as their respiratory samples tested negative. Viral fragments can linger in the body after symptoms disappear, but it doesn’t mean that a person is infectious, or that the disease will make a comeback.

Traditionally, a scientist submits her paper to a journal, which sends it to a (surprisingly small) group of peers for (several rounds of usually anonymous) comments; if the paper passes this (typically months-long) peer-review gantlet, it is published (often behind an expensive paywall). Languid and opaque, this system is ill-suited to a fast-moving outbreak. But biomedical scientists can now upload preliminary versions of their papers, or “preprints,” to freely accessible websites, allowing others to immediately dissect and build upon their results. This practice had been slowly gaining popularity before 2020, but proved so vital for sharing information about COVID‑19 that it will likely become a mainstay of modern biomedical research. Preprints accelerate science, and the pandemic accelerated the use of preprints. At the start of the year, one repository, medRxiv (pronounced “med archive”), held about 1,000 preprints. By the end of October, it had more than 12,000.

The U.S. is now catching up. In April, the NIH launched a partnership called ACTIV, in which academic and industry scientists prioritized the most promising drugs and coordinated trial plans across the country. Since August, several such trials have started.

Researchers have begun to uncover how SARS‑CoV‑2 compares with other coronaviruses in wild bats, the likely reservoir; how it infiltrates and co-opts our cells; how the immune system overreacts to it, creating the symptoms of COVID‑19. “We’re learning about this virus faster than we’ve ever learned about any virus in history,” Sabeti said.

Similar triumphs occurred last year—in other countries. In March, taking advantage of the United Kingdom’s nationalized health system, British researchers launched a nationwide study called Recovery, which has since enrolled more than 17,600 COVID‑19 patients across 176 institutions. Recovery offered conclusive answers about dexamethasone and hydroxychloroquine and is set to weigh in on several other treatments. No other study has done more to shape the treatment of COVID‑19.

SARS‑CoV‑2’s genome was decoded and shared by Chinese scientists just 10 days after the first cases were reported. By November, more than 197,000 SARS‑CoV‑2 genomes had been sequenced. About 90 years ago, no one had even seen an individual virus; today, scientists have reconstructed the shape of SARS‑CoV‑2 down to the position of individual atoms

Respiratory viruses, though extremely common, are often neglected. Respiratory syncytial virus, parainfluenza viruses, rhinoviruses, adenoviruses, bocaviruses, a quartet of other human coronaviruses—they mostly cause mild coldlike illnesses, but those can be severe. How often? Why? It’s hard to say, because, influenza aside, such viruses attract little funding or interest.

COVID‑19 has developed a terrifying mystique because it seems to behave in unusual ways. It causes mild symptoms in some but critical illness in others. It is a respiratory virus and yet seems to attack the heart, brain, kidneys, and other organs. It has reinfected a small number of people who had recently recovered. But many other viruses share similar abilities; they just don’t infect millions of people in a matter of months or grab the attention of the entire scientific community

Thanks to COVID‑19, more researchers are looking for these rarer sides of viral infections, and spotting them.

These factors pull researchers toward speed, short-termism, and hype at the expense of rigor—and the pandemic intensified that pull. With an anxious world crying out for information, any new paper could immediately draw international press coverage—and hundreds of citations.

“There’s a perception that they’re just colds and there’s nothing much to learn,” says Emily Martin of the University of Michigan, who has long struggled to get funding to study them. Such reasoning is shortsighted folly. Respiratory viruses are the pathogens most likely to cause pandemics, and those outbreaks could potentially be far worse than COVID‑19’s.

Their movements through the air have been poorly studied, too. “There’s this very entrenched idea,” says Linsey Marr at Virginia Tech, that viruses mostly spread through droplets (short-range globs of snot and spit) rather than aerosols (smaller, dustlike flecks that travel farther). That idea dates back to the 1930s, when scientists were upending outdated notions that disease was caused by “bad air,” or miasma. But the evidence that SARS‑CoV‑2 can spread through aerosols “is now overwhelming,”

Another pandemic is inevitable, but it will find a very different community of scientists than COVID‑19 did. They will immediately work to determine whether the pathogen—most likely another respiratory virus—moves through aerosols, and whether it spreads from infected people before causing symptoms. They might call for masks and better ventilation from the earliest moments, not after months of debate

They will anticipate the possibility of an imminent wave of long-haul symptoms, and hopefully discover ways of preventing them. They might set up research groups to prioritize the most promising drugs and coordinate large clinical trials. They might take vaccine platforms that worked best against COVID‑19, slot in the genetic material of the new pathogen, and have a vaccine ready within months

the single-minded focus on COVID‑19 will also leave a slew of negative legacies. Science is mostly a zero-sum game, and when one topic monopolizes attention and money, others lose out.

Long-term studies that monitored bird migrations or the changing climate will forever have holes in their data because field research had to be canceled.

negligence has left COVID‑19 long-haulers with few answers or options, and they initially endured the same dismissal as the larger ME community. But their sheer numbers have forced a degree of recognition. They started researching, cataloging their own symptoms. They gained audiences with the NIH and the World Health Organization. Patients who are themselves experts in infectious disease or public health published their stories in top journals. “Long COVID” is being taken seriously, and Brea hopes it might drag all post-infection illnesses into the spotlight. ME never experienced a pivot. COVID‑19 might inadvertently create one

Other epistemic trespassers spent their time reinventing the wheel. One new study, published in NEJM, used lasers to show that when people speak, they release aerosols. But as the authors themselves note, the same result—sans lasers—was published in 1946, Marr says. I asked her whether any papers from the 2020 batch had taught her something new. After an uncomfortably long pause, she mentioned just one.

The incentives to trespass are substantial. Academia is a pyramid scheme: Each biomedical professor trains an average of six doctoral students across her career, but only 16 percent of the students get tenure-track positions. Competition is ferocious, and success hinges on getting published

Conservationists who worked to protect monkeys and apes kept their distance for fear of passing COVID‑19 to already endangered species.

Among scientists, as in other fields, women do more child care, domestic work, and teaching than men, and are more often asked for emotional support by their students. These burdens increased as the pandemic took hold, leaving women scientists “less able to commit their time to learning about a new area of study, and less able to start a whole new research project,

published COVID‑19 papers had 19 percent fewer women as first authors compared with papers from the same journals in the previous year. Men led more than 80 percent of national COVID‑19 task forces in 87 countries. Male scientists were quoted four times as frequently as female scientists in American news stories about the pandemic.

American scientists of color also found it harder to pivot than their white peers, because of unique challenges that sapped their time and energy.

Science suffers from the so-called Matthew effect, whereby small successes snowball into ever greater advantages, irrespective of merit. Similarly, early hindrances linger. Young researchers who could not pivot because they were too busy caring or grieving for others might suffer lasting consequences from an unproductive year. COVID‑19 “has really put the clock back in terms of closing the gap for women and underrepresented minorities,”

In 1848, the Prussian government sent a young physician named Rudolf Virchow to investigate a typhus epidemic in Upper Silesia. Virchow didn’t know what caused the devastating disease, but he realized its spread was possible because of malnutrition, hazardous working conditions, crowded housing, poor sanitation, and the inattention of civil servants and aristocrats—problems that require social and political reforms. “Medicine is a social science,” Virchow said, “and politics is nothing but medicine in larger scale.”

entists discovered the microbes responsible for tuberculosis, plague, cholera, dysentery, and syphilis, most fixated on these newly identified nemeses. Societal factors were seen as overly political distractions for researchers who sought to “be as ‘objective’ as possible,” says Elaine Hernandez, a medical sociologist at Indiana University. In the U.S., medicine fractured.

New departments of sociology and cultural anthropology kept their eye on the societal side of health, while the nation’s first schools of public health focused instead on fights between germs and individuals. This rift widened as improvements in hygiene, living standards, nutrition, and sanitation lengthened life spans: The more social conditions improved, the more readily they could be ignored.

The ideological pivot away from social medicine began to reverse in the second half of the 20th century.

Politicians initially described COVID‑19 as a “great equalizer,” but when states began releasing demographic data, it was immediately clear that the disease was disproportionately infecting and killing people of color.

These disparities aren’t biological. They stem from decades of discrimination and segregation that left minority communities in poorer neighborhoods with low-paying jobs, more health problems, and less access to health care—the same kind of problems that Virchow identified more than 170 years ago.

In March, when the U.S. started shutting down, one of the biggest questions on the mind of Whitney Robinson of UNC at Chapel Hill was: Are our kids going to be out of school for two years? While biomedical scientists tend to focus on sickness and recovery, social epidemiologists like her “think about critical periods that can affect the trajectory of your life,” she told me. Disrupting a child’s schooling at the wrong time can affect their entire career, so scientists should have prioritized research to figure out whether and how schools could reopen safely. But most studies on the spread of COVID‑19 in schools were neither large in scope nor well-designed enough to be conclusive. No federal agency funded a large, nationwide study, even though the federal government had months to do so. The NIH received billions for COVID‑19 research, but the National Institute of Child Health and Human Development—one of its 27 constituent institutes and centers—got nothing.

The horrors that Rudolf Virchow saw in Upper Silesia radicalized him, pushing the future “father of modern pathology” to advocate for social reforms. The current pandemic has affected scientists in the same way

COVID‑19 could be the catalyst that fully reunifies the social and biological sides of medicine, bridging disciplines that have been separated for too long.

“To study COVID‑19 is not only to study the disease itself as a biological entity,” says Alondra Nelson, the president of the Social Science Research Council. “What looks like a single problem is actually all things, all at once. So what we’re actually studying is literally everything in society, at every scale, from supply chains to individual relationships.”

Only 2% of the patients in a review of nearly 45,000 confirmed Covid-19 cases in China were children, and there were no reported deaths in children under 10

Among nearly 6,300 Covid-19 cases reported by the Korea Centers for Disease Control & Prevention on March 8, there were no reported deaths in anyone under 30. Only 0.7% of infections were in children under 9 and 4.6% of cases were in those ages 10- to 19-years-old.

Studies from China show that the rate of deaths for those with cardiovascular issues is 10.5% while it’s 7.3% for diabetes patients and about 6% for those with hypertension or lung and respiratory disease. In cancer patients, it was reported as 5.6%.

Is Covid-19 more contagious than influenza or other viral respiratory diseases? It appears to be. Both are very contagious. The R0—pronounced “R naught”—is an estimate of how many healthy people one contagious person will infect. The R0 for Covid-19 is estimated to be 2.6. “That’s a lot,” says Dr. Schaffner.

A high fever would be 101 or higher

Are there any precautions or steps different in coronavirus prevention than in influenza prevention? What about treatment? No. Both illnesses are infectious respiratory illnesses caused by different viruses but spread the same way, says Vanessa Raabe, an infectious disease specialist at NYU Langone Health. They are transmitted through droplets from a sick person sneezing or coughing or talking within 2 meters or 6 feet. If such a droplet enters your eyes, mouth or nose, you could become infected.

There is some concern that the new coronavirus can also be transmitted by tiny fine droplets that remain suspended in the area after an ill person leaves, but Dr. Raabe says that it’s not believed to be the main way it’s transmitted and it’s more of a worry in the health care setting.

Do allergy and asthma sufferers have a higher rate of illness contraction? There is no evidence that allergy sufferers have a higher rate of getting the new coronavirus. But asthma suffers do. The groups with the highest risk of fatalities are the elderly and those with diabetes, heart disease, lung disease, including respiratory illnesses, and smokers

When should I go to the hospital? Experts say you should go to a hospital if you’re sick enough that you think you should be admitted. The telltale sign is difficulty breathing or shortness of breath combined with a high fever

shortness of breath and difficulty breathing is a sign that the lungs are being affected and the virus has moved from being an upper tract respiratory illness to a lower tract one. Upper tract illness is usually defined by a runny nose, congestion, and sore threat. Once a virus moves to the lower tract symptoms can include shortness of breath and a lot of coughing that produces mucus

In comparison, for influenza the figure is somewhere around 1.2 to 1.8

How do you distinguish the new coronavirus from the flu or the common cold? It’s impossible to do based on symptoms alone, says Dr. Raabe. The main symptoms of the new coronavirus are fever, cough, shortness of breath, and general fatigue and muscle aches. These overlap with the symptoms of the flu or any other respiratory virus. The only way to know for sure is to get tested by a doctor

The coronavirus vaccines, in contrast, are injected deep into the muscles and stimulate the immune system to produce antibodies. This appears to be enough protection to keep the vaccinated person from getting ill.Some of those antibodies will circulate in the blood to the nasal mucosa and stand guard there, but it’s not clear how much of the antibody pool can be mobilized, or how quickly. If the answer is not much, then viruses could bloom in the nose — and be sneezed or breathed out to infect others.

“It’s a race: It depends whether the virus can replicate faster, or the immune system can control it faster,”

The coronavirus vaccines have proved to be powerful shields against severe illness, but that is no guarantee of their efficacy in the nose. The lungs — the site of severe symptoms — are much more accessible to the circulating antibodies than the nose or throat, making them easier to safeguard

Pfizer will test a subset of its trial participants for antibodies against a viral protein called N. Because the vaccines have nothing to do with this protein, N antibodies would reveal whether the volunteers had become infected with the virus after immunization, said Jerica Pitts, a spokeswoman for the company.

Only people who have virus teeming in their nose and throat would be expected to transmit the virus, and the lack of symptoms in the immunized people who became infected suggests that the vaccine may have kept the virus levels in check.

Vaccinated people who have a high viral load but don’t have symptoms “would actually be, in some ways, even worse spreaders because they may be under a false sense of security,” Dr. Maldonado said.

South Korea’s economy is expected to decline by just 0.8% this year, the best among the Organization for Economic Cooperation and Development’s forecasts for member nations.

When the supply of face masks ran short early on in the crisis, the government seized production.

The nation fast-tracked approval of domestic testing kits as soon as cases began hitting

It tapped into its relative wealth and hyperconnectivity, blasting text alerts to citizens if infections occurred in their area

The key to South Korea’s success came from blending technology and testing like no other country, centralized control and communication—and a constant fear of failure.

Some parts of its playbook wouldn’t work in most Western societies—and received backlash in South Korea as well

Nearly everyone in the country wears masks.

Every confirmed patient, even those with no or mild symptoms, gets isolated at hospitals or converted dormitories run by the government. Treatment is free.

As a result, South Korea never had to mandate a lockdown, so restaurants and business were able to stay open, cushioning the blow to the economy.

“No country has adapted to living with, and containing, the virus like South Korea,”

“You don’t need or want to eradicate the virus. But you modify your behavior and get on with life.”

It detected the country’s first case 10 days later using a test that screened for all known coronavirus strains—the same tactic practiced during the December simulation.

Health officials have unfettered access to individuals’ private mobile data, and early on used government websites to share the whereabouts of confirmed patients, plucked from smartphone GPS history

The government now offers anonymous testing and leaves out identifying information and specific names of places visited in contact-tracing disclosures.

After a major cluster linked to a megachurch in the city of Daegu emerged on Feb. 18, the government made a flurry of moves

Cases peaked in 11 days.

The day after cases reached a five-month high of 441 on Aug. 27, South Korea’s top public-health official gave a grim forecast: “We could see 800 to 2,000 infections next week

South Koreans took the advice and adjusted. Population mobility, as measured by local telecom operators, soon fell by one-quarter. Most schools closed and diners had to leave restaurants by 9 p.m. Aug. 27 turned out to be the peak.

At twice-a-day briefings, health officials express worry when they can only trace the origins of three-quarters of confirmed cases.

In total, South Korea, with a population of 52 million, has reported 23,455 cases and 395 deaths.

One reason South Korea was prepared: It learned painful lessons in 2015 from an outbreak of Middle East respiratory syndrome

“The only way to make the government prepared is to actually have an outbreak,”

After MERS, the government started twice-a-year training sessions simulating a rapid spread of viral disease

“Oddly enough, last December’s ‘war game’ was a novel coronavirus,”

After two weeks of aggressive social distancing, South Koreans could again head back to schools, gyms and sports stadiums.

One firm, Kogene Biotech Co., demonstrated a successful test and got the regulatory green light within four days. A second manufacturer would be added by Feb. 12. The tests all used the same methodology and could be sent to any of the country’s roughly 120 laboratories that promised turnaround times of between six to 24 hours.

Cases, which had been slowly rising, suddenly doubled in a day, to over 100. Experts predicted it would soon surge to levels seen nowhere else but China.

That triggered a Feb. 20 late-night message in a group chat with eight South Korean infectious-disease experts: “We need to quickly devise a way to conduct mass testing,”

an answer: drive-through clinics.

Dr. Kim sent a PowerPoint presentation to the group within hours, at 3:53 a.m., outlining how tests would take just 10 minutes and saved much-needed protective gear since outdoor workers didn’t have to change gowns after each patient

Two days later, cars rumbled through the country’s first drive-through clinic. Testing capacity multiplied 100 times, giving South Korea a critical early edge.

As South Korea’s coronavirus problems mounted, Mr. Moon intentionally kept his profile low. “His stance is that it’s more objective for an expert to hold the briefings, and that is the way to gain the trust of the people,”

Even with the swift response, a lack of hospital beds became a major issue. In just 11 days, South Korea’s case count had gone from 31 to 3,150. Thousands were waiting to be hospitalized. A handful died while waiting.

South Korea’s infectious-disease experts had a proposal. Confirmed patients should be divided into four categories, based on the risk profile and severity of symptoms, with only the most serious cases hospitalized. Those with mild or no symptoms should be isolated at makeshift treatment facilities.

Dr. Peck set up a meeting with senior officials from the Samsung conglomerate, asking that an empty facility near Daegu be lent to the South Korean government. By first having a company volunteer a venue, Dr. Peck recalled thinking, it would pressure South Korea’s health ministry to act.

About 80% of South Korea’s coronavirus patients have been hospitalized in the community treatment centers. Those who are asymptomatic or have mild symptoms are still sent there.

That changed in August. Unlike February’s outbreak, the new wave of infections fanned out across South Korea to all 15 of the country’s major cities and provinces. The country’s national testing capacity had by then expanded to 50,000 a day with test results notified within 24 hours, up from 20,000 in February

The U.S. conducted about 900,000 tests a day over the past week through Thursday, according to data from the Covid Tracking Project. But South Korea performs six times as many tests per confirmed Covid-19 case than the U.S. doe

South Korea’s three-tier system created in June for social distancing went off script. With health experts split on whether to adopt the maximum levels last month, a government advisory committee landed at a “level 2.5” social-distancing for the Seoul area that closed schools and banned church services and gatherings of more than 10 people.

On Tuesday, South Korea reported its lowest one-day infections in over a month, with just 61 cases.

“I guess an email is notification of exposure,” said Erin Sanders, a nurse practitioner and certified contact tracer in Boston. “But that is not contact tracing,” she said, “and not how a responsible public health agency handles a super-spreading cluster of a deadly virus.”

an internal C.D.C. email on Friday asked the agency’s scientists to be ready to go to Washington for contact tracing, but a request from the White House for assistance never came, according to two senior C.D.C. scientists.

Experts at the C.D.C. could have immediately put in place contact tracing for President Trump and others who have been infected, working with health departments of the states to which Mr. Trump and others have traveled. But regulations require that the C.D.C. be asked to step in.

During the 48-hour window before Mr. Trump’s diagnosis that White House contact tracers are focusing on, the president debated former Vice President Joseph R. Biden Jr. in Cleveland; traveled to a rally of thousands in Minnesota; met with supporters and donors at his golf club in Bedminster, N.J.; and conferred with dozens of aides at the White House, all while not wearing a mask.

The timing of the diagnosis of Mr. Trump’s illness makes it highly likely that he and the others became infected on Saturday, medical experts said. Symptoms typically appear around five days after exposure to the virus; Mr. Trump began showing symptoms on Thursday, “right smack dab in the day” he would be expected to, Dr. Maldonado said.

“Staff should not go to the White House Medical Unit clinic for any Covid-19 testing inquiries,” the memo said. But some officials have continued to go to work.

The United Kingdom’s National Health Service recommends swabbing both the nose and the throat when using a rapid antigen, or later flow, Covid test, the kind used at home.

“The virus grows in your nose and throat and somewhat at different time scales,” Michael Mina, chief science officer for the biotech software company eMed, who was an assistant professor of epidemiology at the Harvard T.H. Chan School of Public Health, said at a testing technology news briefing this week.

“The agency recommends that individuals closely follow the tests’ instructions,” FDA spokesperson Jim McKinney told NBC News in an email.

Dr. Jonathan Li, an infectious disease physician at the Brigham and Women’s Hospital in Boston, cautions against altering the testing strategy that has been validated and authorized by the FDA.

“What we’ve learned is that every variant seems to have its own characteristics, and it’s important that we not be locked into thinking we know everything based on what we’ve learned from the last variant,” he said

Before advocating the altered approach, Li said, he would need to see data that showed it was effective. User error will likely be higher with self-administered throat swabs compared with nasal swabs, he said.

“The nose and the throat have different pH levels and we have seen people take Coke or coffee and put it in an antigen test and had a line to appear,” she said. “We don’t know exactly why this happens, but the hypothesis is acidity.” 

Miller notes that a small preprint paper out of South Africa, which has not yet been peer-reviewed, suggested that more detectable virus may reside in the throat than in the nose when a person is infected with omicron compared to the delta variant, though the study compared PCR to antigen, or rapid, tests, which are not the same type of tests. 

Miller said that although she would not be surprised if omicron indeed does show up in the throat before it does in the nose, that concrete data has yet to be shown. 

According to Matt Binnicker, director of clinical virology at the Mayo Clinic, the fact that positivity rates are soaring in the U.S. is a testament to how well Covid tests are still working.

According to Miller, it’s best to take a rapid test on day one, day two and day three of symptoms if you are testing negative but your symptoms persist. You should also isolate. “If you have symptoms, you have Covid until proven otherwise,” she said. 

there are no psychologists who specialize in exposure and response prevention, the specific kind of therapy she and many others with OCD require in order to break their crippling thought cycles.

At its worst, OCD can compel people to spend hours each day rehearsing an intricate mental dance they feel powerless to end.

Along with medication, exposure and response prevention, or ERP, therapy is the gold-standard treatment for people with OCD. It is radically different from more traditional talk therapy, which excavates patients’ childhoods or past relationships for clues to their present-day problems.

a person is forced to confront their obsessive thoughts relentlessly. The goal is to make the sufferer so accustomed to their obsessions that they no longer feel tempted to engage in soothing compulsions.

Because the symptoms can be entirely mental, it can take years for either patients or therapists to recognize OCD for what it is.

ERP teaches people, “these thoughts are meaningless, you need to learn to ignore them.”

some studies estimate it takes OCD sufferers 17 years to find proper treatment from the onset of symptoms. Seeking certain forms of talk therapy can make them worse, not better. In the meantime, some experience symptoms so debilitating they are confined to their homes.

Most moderate OCD cases get at least partly better if the patient receives two or three months of ERP.

There is no mandatory number of hours that psychologists must spend training in either cognitive-behavioral therapy or ERP, said Lynn Bufka, a psychologist with the American Psychological Association. Bufka did not know what percentage of psychotherapists provide ERP, but she suspects it’s “small.”

Between 3 and 7 million Americans suffer from OCD at some point—a substantial number, but still far fewer than the vast multitudes who seek therapy for anxiety and depression.

People obsessed with not offending God might hold a satanic ritual. Those assailed by persistent (and baseless) fears they will molest their siblings might read the incest tome Flowers in the Attic.

Access to ERP therapists is compounded by the already profound shortage of psychotherapists in rural areas. More than half of U.S. counties have no mental-health professionals at all.

ERP specialists might feel no need to take insurance, since they are so rare they often have no shortage of clients, Szymanski, of the International OCD Foundation, pointed out.

But the treatment was so expensive it contributed to the family’s decision to sell their house.

Chan, whose agency was assailed as too slow in reacting to West Africa's Ebola epidemic that killed more than 10,000 people in the past two years, cited "first and foremost the big concern about microcephaly," the birth defect that causes babies to be born with abnormally small heads and improperly developed brains.

U.S. Centers for Disease Control and Prevention (CDC) head Thomas Frieden said the WHO emergency declaration "calls the world to action" on Zika. The CDC added four more countries and territories to its list of locales that pose a risk for Zika infection, advising pregnant women to consider avoiding travel to those areas.

Brazil is due to host the Olympics in Rio de Janeiro in August, and President Dilma Rousseff's chief of staff said on Monday there is no risk of cancelling the games due to Zika.

The emergency designation, recommended by a committee of independent experts following criticism of a hesitant response to Zika so far, should help fast-track international action and research priorities. The move lends official urgency to research funding and other steps to stem the spread of the virus.

This marks the fourth time the WHO has declared a global health emergency since such procedures were put in place in 2007, with the others arising from influenza, Ebola and polio.

The Zika virus has raised questions worldwide about whether pregnant women should avoid infected countries. Chan said delaying travel was something pregnant women "can consider" but added that if they needed to travel they should take protective measures by covering up and using mosquito repellent.

Brazil has reported some 3,700 suspected cases of microcephaly. Brazilian Health Minister Marcelo Castro told Reuters the epidemic was worse than believed because in 80 percent of cases the infected people had no symptoms.

As the virus spreads from Brazil, other countries in the Americas are also likely to see cases of babies with Zika-linked birth defects, experts believe. The clinical symptoms of Zika are usually mild and often similar to dengue, which is transmitted by the same mosquito, leading to fears that Zika will spread into all parts of the world where dengue is commonplace.

More than a third of the world’s population lives in areas at risk of dengue infection, in a band stretching through Africa, India, Southeast Asia and Latin America.Zika's rapid spread in Latin America is attributed to the prevalence of Aedes aegypti and a lack of immunity among the population.

A senior Obama administration official, speaking on condition of anonymity, said, "This is not an Ebola-type situation where you have to stop people at the border."

New York State Governor Andrew Cuomo said the state's health department would offer free tests for individuals with symptoms of infection who have traveled to countries impacted by Zika.

El Salvador’s Health Ministry is particularly concerned about the rise of cases of Guillain-Barré syndrome, which leads to paralysis, usually temporary; researchers are exploring a possible link between Guillain-Barré and Zika. Forty-six suspected cases of the syndrome had been reported as of last week, Violeta Menjívar, the health minister, said in a radio interview.

virus has appeared in only three Mexican states. The mosquitoes that carry the virus, he said, could not survive in the high altitudes of the central plateau, including Mexico City.“I think it’s good to have these warnings,” he said, “but these things should be explained to people.”

Their model for Zika’s possible spread, using worldwide temperature profiles and air travel routes, also determined that more than 60 percent of the population in the United States lives in areas conducive to seasonal Zika transmission. And about 23 million people in the United States live in places with climates like Florida and parts of Texas where Zika can be transmitted by mosquitoes year-round, the researchers said.The authorities in Brazil insist that they are taking steps to fight Zika, including vaccine research.

Public health laboratories in all 50 states and Washington, D.C. are now testing for the coronavirus and many more labs are completing testing verification procedures outlined by the Federal Drug Administration. But some states are actively discouraging testing for anyone who is not showing symptoms, and a request from a doctor is no guarantee of a test, Dr. LeRoy said.

The state labs are largely being used for patients identified by the Centers for Disease Control and Prevention as high priority. This includes hospitalized patients with symptoms compatible with the coronavirus; those over 65; those with chronic medical conditions or compromised immune systems; those who show symptoms within 14 days of being in contact with a confirmed coronavirus patient; and those with a history of travel to China, Italy, Iran or South Korea.

Preparation is the key to a good plan.

Hopefully, you've been following standard hygiene practices. These are behaviors we should be doing daily, automatically, to protect ourselves from germs, colds and flu:

Avoid touching your eyes, nose and mouth with unwashed hands; cough and sneeze into elbows or tissues that you immediately throw away, and regularly wash, wash, wash those hands with warm water and lots of soapy bubbles.

Parents and guardians should plan well in advance by setting up a structure in which all kids and potential caregivers know their roles and expectations, said pediatrician Dr. Tanya Altmann, Editor-in-Chief of the American Academy of Pediatrics' book "Caring for Your Baby and Young Child: Birth to Age 5 and The Wonder Years."

A working thermometer to monitor fever, which is considered to be 100 degrees Fahrenheit (37.7 degrees Celsius), and a method to clean it, such as Isopropyl alcohol.

Fever reducing medications, such as acetaminophen.

Regular soap and 70% alcohol-based hand sanitizer (antibacterial soap isn't necessary if you wash properly, and that way you won't will contribute to the world's growing antibiotic-resistant superbugs).

Tissues to cover sneezes and coughs. But there's really no need to hoard toilet paper -- this is a respiratory disease.

Regular cleaning supplies, kitchen cleaning gloves and trash can liners.

Disinfectant cleaning supplies -- the CDC suggests picking from a list that meets the virus-fighting standards of the US Environmental Protection Agency, but says you can also make your own version by using 1/3 cup unexpired bleach per gallon of water or 4 teaspoons bleach per quart of water. Never mix bleach with ammonia or any other cleanser -- it produces toxic gases.

If you live alone, that's not difficult. Your challenge is to monitor your symptoms and care for yourself when you're not feeling well. Be sure to have a plan in place to deliver food and medications, and find someone who can be responsible for virtually checking in on you on a regular basis.

The rest of the family should practice isolation as well, Radesky added.

If you are running short on face masks, or don't have any because of hoarding, try to protect the caregiver as best you can, the CDC says.

Altmann stresses maximizing isolation and protective actions.

"You can have a healthy person leave the sick one food and drinks at the door, and then go wash their hands," Altmann explained. "Wear gloves to pick up the empty plates, take them back to the kitchen and wash them in hot water with soap, or preferably with a dishwasher, and wash your hands again."

One last, very important thing: Call 911 immediately if you or your loved ones have any of these symptoms: increased or sudden difficulty breathing or shortness of breath; a persistent pain or pressure in the chest; and any sign of oxygen deprivation, such as new confusion, bluish lips or face, or you can't arouse the sick person.

To be clear: Everyone in the house needs to isolate themselves from the outside world as much as possible.