Tag Archives: Asymptomatic

World

Shanghai lockdown deepens after new surge in asymptomatic COVID cases

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SHANGHAI, April 5 (Reuters) – The major Chinese financial centre of Shanghai extended restrictions on transportation on Tuesday after a day of intensive city-wide testing saw new COVID-19 cases surge to more than 13,000, with no end to the lockdown in sight.

After originally taking a more piecemeal approach aimed at minimising economic disruptions, Shanghai imposed broader restrictions last week as authorities struggled to contain what has become the city’s biggest COVID-19 outbreak.

The lockdown now covers more than 25 million people after restrictions in the city’s western districts were extended until further notice in what has become a testing ground for the government’s zero-tolerance “dynamic clearance” approach and its ability to contain the highly infectious Omicron variant.

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“Currently, Shanghai’s epidemic prevention and control is at the most difficult and most critical stage,” said Wu Qianyu, an official with the municipal health commission, at a Tuesday briefing. “We must adhere to the general policy of dynamic clearance without hesitation, without wavering.”

Shanghai reported a record 13,086 new asymptomatic coronavirus cases on April 4, the city government said on its official WeChat channel, up from 8,581 the previous day, after a city-wide surveillance testing programme that saw more than 25 million people swabbed in 24 hours.

The local government said it had collected 25.67 million samples in 2.4 million test tubes on Monday, and almost 80% of the total had been tested by 8:00 on Tuesday morning. Any positive results are followed up at the individual level.

Symptomatic cases fell on Monday to 268, from 425 a day earlier. The proportion of official symptomatic infections remains far lower than the rest of the world, which experts have attributed to the city’s proactive screening process.

At least 38,000 personnel have been deployed to Shanghai from other regions in what state media has described as the biggest nationwide medical operation since the shutdown of Wuhan in early 2020 after the first known coronavirus outbreak.

Authorities said late on Monday that further restrictions would be placed on the city transportation networks from Tuesday, with more subway lines suspended.

DRACONIAN MEASURES

Thousands of Shanghai residents have been locked up in rudimentary “central quarantine” facilities after testing positive, whether they are symptomatic or not.

Jane Polubotko, a Ukrainian marketing manager now held in the city’s biggest quarantine centre, told Reuters that it was still unclear when and how they would be released.

“Nobody knows how many tests we need to get out,” she said.

As members of the public continued to express concerns about Shanghai’s draconian measures, sharing videos across social media, Sun Chunlan, China’s vice-premier in charge of COVID prevention, urged grassroots Party organisations to “do everything possible” to help residents solve their problems, such as access to medicine, food and water.

Analysts outside China have been warning about the economic costs of the country’s unyielding campaign to curb infections.

“What is most striking in Shanghai is the difficulty that the authorities are having in managing logistics, particularly conditions in centralised quarantine facilities,” said Michael Hirson, China analyst with the Eurasia Group consultancy.

“Given that Shanghai has a highly capable government, current problems pose a warning for local governments across China where capacity is not as high and major outbreaks could stretch resources further to the limits,” he added.

Nationwide, China reported 1,235 confirmed coronavirus cases for April 4, down from 1,405 a day earlier, including 1,173 local transmissions. The number of new asymptomatic cases stood at 15,355, compared with 11,862 a day earlier.

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Reporting by David Stanway and Brenda Goh; Editing by Stephen Coates and Richard Pullin

Our Standards: The Thomson Reuters Trust Principles.

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World

Explainer-Why are Shanghai’s COVID infections nearly all asymptomatic?

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By David Stanway

SHANGHAI (Reuters) – Epidemiologists examining the biggest Chinese outbreak of COVID-19 in two years are trying to ascertain why the proportion of asymptomatic cases is so high, and what it could mean for China’s future containment strategy.

The number of new confirmed community transmitted cases in the major financial hub of Shanghai reached 4,477 on Tuesday, a record high, but only 2.1% showed symptoms. The share of symptomatic cases over the previous seven days was around 1.6%.

Although outbreaks overseas have demonstrated that Omicron was less deadly than its predecessors, with lower levels of hospitalisation, the rate of symptomatic infection was relatively high compared to China’s numbers.

In Britain, estimates for the share of asymptomatic Omicron infections have ranged between 25% and 54%, government data shows, although testing has not been systematic.

Britain has also been ahead in lifting all restrictions as it and other countries adapt a policy of living with COVID while the Chinese government has remained cautious and international travel is still curtailed.

The lack of symptomatic infections in the country and the very low number of deaths – only two related to COVID this year – has raised hopes that China can achieve a “soft landing” when it eases “dynamic clearance” restrictions as it refers to a policy of lockdowns and mandatory testing.

Following are some explanations for why the rate of asymptomatic cases is so high.

SURVEILLANCE TESTING

China is also the only major country to do mass, untargeted surveillance testing, which is bound to uncover more asymptomatic cases, although it could also be expected to reveal more symptomatic cases.

“Surely, high levels of testing will pick up more rather than less asymptomatic cases,” said Adrian Esterman, an expert in biostatistics at the University of South Australia.

In other countries, many people who test positive with home kits do not report it and official data also shows falls in infections outside China have coincided with a decline in the number of tests carried out.

On Monday alone, Shanghai conducted more than 8 million tests at over 60,000 stations throughout its locked down districts. Other countries, even if they still impose mandatory testing programmes, now take a more targeted approach.

LOWER VIRULENCE, HIGHER VACCINATION

China’s uncompromising response to the new variant was partly a result of uncertainty about levels of immunity and resistance among the population after nearly two years of heavy containment.

But writing on the Twitter-like Weibo platform last week, Shanghai COVID expert Zhang Wenhong said that while the new Omicron variant was harder to eliminate, it was clearly less “scary” than its predecessors.

Chinese experts, including Zhang Boli, who advises the government on COVID-19 treatment, have said the inherently lower pathogenicity of Omicron, combining with the country’s relatively high vaccination rates, could be lowering the number of symptomatic infections.

However, vaccination levels in South Korea and Singapore are higher than in China, and they have more symptomatic cases.

CATCHING IT EARLY

Zhang also said in an interview with China’s Science and Technology Daily on Tuesday that the large proportion of asymptomatic infections was not necessarily a characteristic of the virus itself.

The high rate could be a result of early detection in China, allowing authorities to catch and isolate cases before they became symptomatic, and it was still possible that large numbers of people could get ill.

Wu Zunyou, chief epidemiologist of the China Center for Disease Control, told a press conference on Saturday that “asymptomatic” was not a fixed state. People could start to get ill within days and attention still needed to be paid to the infection rate, he said.

CO-INFECTIONS

It is also possible that many of the symptoms that are being picked up in overseas cases are caused by “co-infections”, with particularly virulent strains of the common cold often presenting in similar ways to COVID-19.

Researchers said that lockdowns overseas led to a noticeable decline in other infectious diseases, including influenza. With much of world now learning to “coexist” with COVID, there has also been an opportunity for old viruses to make a comeback.

(Reporting by David Stanway; editing by Barbara Lewis)

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Health

Exercise Is Good for You, Even if You Have a Mild Case of Covid

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To exercise with Covid or not—that’s the question some fitness buffs are asking. The American College of Sports Medicine has suggested people under 50 who experience mild or no symptoms to rest for at least seven to 10 days after testing positive. Their recommendation appears to be motivated by the concern that even a mild Covid-19 infection may damage the heart and potentially cause sudden death during physical exertion.

There’s little evidence to support this recommendation. Because exercise boosts the immune system, it may even help people bounce back faster from Covid.

Viral infections, including those that cause the flu and the common cold, are a major cause of myocarditis, the inflammation of the heart muscle. The condition can cause chest pain and irregular heartbeat, though it is often asymptomatic. This makes its prevalence hard to measure. According to some estimates, 1% to 5% of all people with acute viral infections may develop myocarditis.

Yet sudden death from myocarditis during physical activity appears to be rare. A study from 1980 to 2006 documented 41 sudden deaths in young athletes (under 40) linked to myocarditis—one-tenth as many as from blunt trauma.

Some experts feared Covid-19 would increase cardiac risk in otherwise young and healthy people. A study early in the pandemic from Germany reported signs of myocarditis in 60% of Covid-19 patients, including some with relatively mild illness. But criticisms of the study’s design and data errors prompted more investigation, and recent studies have been mostly reassuring.

In one study, cardiac tests were performed on 789 professional athletes (soccer, baseball, basketball, football and hockey) with prior infections, most of whom had mild or no Covid symptoms. Only five (0.6%) had inflammation on cardiac imaging—in line with estimates for other viral infections—and all of them had symptoms that the researchers said “exceeded empirical definitions of mild COVID-19 illness” such as cough, fatigue or loss of taste.

In another study, only 0.7% of 3,018 college athletes who tested positive for Covid had abnormal cardiac test results that researchers believed were definitely, probably or possibly linked to the virus. (Extremely fit athletes are known to have “remodeled” hearts that can cause abnormal findings on cardiac tests. That makes it hard for cardiologists to tell if the abnormalities result from the virus.)

A third study, involving 3,597 college athletes who had tested positive with symptoms ranging from none to chest pain and shortness of breadth, found that only 1.2% experienced symptoms that persisted for more than three weeks. Only 4% experienced heart- or lung-related symptoms when they returned to exercise. Yet the vast majority of those who underwent more testing didn’t show evidence of cardiac damage from Covid-19, and it’s normal to experience fatigue or shortness of breath when returning to exercise after a flulike illness.

Studies on young competitive athletes are easier to perform than on the general population, and they may not be 100% applicable to recreational athletes. Still, they show that otherwise healthy and fit people who catch Covid are unlikely to suffer cardiac complications.

A recent study of U.K. healthcare workers found those who had mild or no Covid symptoms were no more likely to have cardiac abnormalities on tests six months after infection than those who hadn’t been infected. “This study demonstrates that in healthy people, measured cardiovascular abnormalities are common, but no more common in those who had had mild SARS-CoV-2 6 months previously compared with those who had not,” the researchers found.

The seven- to 10-day rest recommendation appears to be as arbitrary as the six-foot social distancing from early in the pandemic. Most people who don’t know they have Covid won’t follow it anyway.

“There is very little good quality data on exercise resumption post-Covid,”

Gabriel Vorobiof,

a cardiologist at UCLA, says in an email. “At one point there was a big controversy when a few cardiac MRI papers showed some potentially concerning cardiac findings post-Covid.” But since the studies didn’t include a control group for comparison—such as athletes or young people without Covid who get an MRI—he says the “findings were later dismissed as associations, not necessarily causative links.”

He adds: “I’ve seen quite a few young athletes requiring ‘cardiac clearance’ by their sporting club after having uncomplicated Covid prior to re-engaging in their respective sports, many of which were noncompetitive. The need to clear a young person following an asymptomatic viral illness, like many things during this pandemic, seems to be an overreaction based on little if any science.”

Doctors generally advise people with head colds that they may exercise, but should listen to their bodies. This seems like sensible advice for otherwise healthy people with mild Covid. “However, if symptoms of chest pain or discomfort, lightheadedness or palpitations arise, one should stop and seek medical attention,” Dr. Vorobiof says.

Exercise has been found to protect people from other viral infections, including flu, herpes, Epstein-Barr and the common cold, and improve the immune response to vaccinations. Each workout mobilizes billions of immune cells, especially the T-cells that circulate, identify and kill virus-infected cells. Exercise also reduces levels of the stress hormone cortisol, which impairs white blood cells and increases inflammation.

As people learn to live with Covid, there’s no reason they shouldn’t work out with it too.

Ms. Finley is a member of the Journal’s editorial board.

Wonder Land: The weaponization of ‘science’ began with climate policy and accelerated with Covid-19. Now many think it’s all misinformation. Images: AFP/Getty Images Composite: Mark Kelly

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Health

Even asymptomatic COVID could lead to long-term damage- study

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Even a mild case of COVID-19 could trigger an immune response that lasts longer than the initial infection and recovery, according to new research carried out by scientists at Cedars-Sinai Medical Center in Los Angeles.
The findings were published in the Journal of Translational Medicine, in the first study to report not only the presence of elevated autoantibodies after mild or asymptomatic infection, but also their persistence over time.

When people are infected with a virus or other pathogen, their bodies unleash proteins called antibodies that detect foreign substances and keep them from invading cells. In some cases, however, people produce autoantibodies that can attack the body’s own organs and tissues over time. The findings, which are based on 177 people with confirmed evidence of a previous COVID-19 infection, reveal that people with a prior infection of SARS-CoV-2, the virus that causes COVID-19, have a wide variety of autoantibodies up to six months after they have fully recovered.

“These findings help to explain what makes COVID-19 an especially unique disease,” said Justyna Fert-Bober PhD, co-senior author of the study. “These patterns of immune dysregulation could be underlying the different types of persistent symptoms we see in people who go on to develop the condition now referred to as long COVID-19.”

Israeli soldier line up in a queue at the entrance of a COVID-19 rapid antigen Magen David Adom testing center in Jerusalem on January 03, 2022. (credit: OLIVIER FITOUSSI/FLASH90)

The researchers noted that they intend to expand the study to look for the types of autoantibodies that may be persistent in people with long-haul COVID-19 symptoms.

It remains unclear whether autoantibodies are similarly made in people with breakthrough infections because the study was conducted before vaccines were rolled out.



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Sports

Green Bay Packers QB Aaron Rodgers asymptomatic from COVID-19, has met return-to-play protocols

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GREEN BAY, Wis. — Aaron Rodgers has remained asymptomatic from COVID-19 and has met the NFL/NFLPA return-to-play protocols, sources told ESPN’s Adam Schefter.

All that is left now is for the Green Bay Packers to officially activate him by 4 p.m. ET on Saturday in order for him to play Sunday against the Seattle Seahawks at Lambeau Field.

Rodgers concluded his 10-day quarantine required for unvaccinated players who test positive for the virus.

Packers coach Matt LaFleur said Friday Rodgers fully participated in all meetings this week virtually.

“It’s been going great,” Packers coach Matt LaFleur said this week of the preparation for Sunday. “Communication’s been there. He’s been in every meeting. He’s been engaged. So, it’s just he’s not with his guys out on the field. That’s the dynamic that you never know. But we’re fortunate to have a guy that has got a ton of reps under his belt, has played a ton of ball, so we’re pretty confident that provided he checks out well he can go out there and play at a high level.”

Rodgers was not allowed back in the team facility until Saturday but indicated he had been working out on his own. During his weekly appearance on The Pat McAfee show, said Tuesday that he would ramp up his conditioning on his own as the week went on and said he believed there was only a “small possibility” that he would not play Sunday.

“I just do believe there’s a health hurdle that I have to [clear] as far as like movement and sweating and getting into it, making sure my body, especially heart, is fine with physical exertion,” Rodgers said.

Receiver Davante Adams, who returned last week after his positive COVID-19 test, said he noticed a difference in his endurance in his first game back Sunday against the Chiefs.

“I don’t know how it’ll impact Aaron or the quarterback position; it’s much different movements,” Adams said. “But I definitely was a little bit more taxed in the game than I usually would be. It kind of felt like Week 1 all over again.

“Wasn’t anything crazy, and I don’t think it was the COVID that did it. It was more so me stationary, not moving around for 10 days, which doesn’t seem crazy, but when you’re moving every day and getting the conditioning that we get as wideouts, you definitely notice a difference.”

The Packers lost at the Kansas City Chiefs, 13-7, last Sunday in Jordan Love’s first NFL start.

LaFleur prepared Love as if he will start again this week just in case there were issues upon Rodgers’ return.

When asked on Friday whether he expected Rodgers to start, LaFleur said: “Yeah, but you know, a lot of things [can] happen. So just like we told Jordan, ‘You’ve got to be ready to go.’ And if that’s the route we go, then he’ll be ready.”

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Health

Fully Vaccinated Almost Twice As Likely to Be Asymptomatic

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  • Fully vaccinated people who caught COVID-19 were twice as likely to get no symptoms, a study found.
  • But most vaccinated people in the study didn’t catch COVID-19. 
  • Study authors said vaccinated people who interacted with vulnerable people should get regular tests.

Fully vaccinated people that catch COVID-19 are almost twice as likely to get no symptoms than those who haven’t had a vaccine, a large UK study suggests.

The study from researchers at King’s College London was published in The Lancet Infectious Diseases medical journal late Wednesday. It found that fewer than 0.2% of 971,504 fully vaccinated adults studied caught COVID-19 at least a week after their second dose.

But, for the 2,370 who did get infected post-vaccination, the likelihood of having no symptoms increased by 94% compared to someone who’s unvaccinated, the study authors said.

The scientists also found that the likelihood of catching COVID-19 with five or more symptoms in the first week of illness was reduced by about a third in those fully vaccinated. The likelihood of getting hospitalized with COVID-19 after two doses of a COVID-19 shot was reduced by two-thirds, they said. 

The study authors said that the findings highlighted the importance of regularly testing vaccinated people regardless of symptoms. This was especially the case if they interacted with unvaccinated people or those vulnerable to COVID-19, such as those who are older or with underlying health conditions.

Dr. Claire Steves, co-lead study author, said in a statement that the findings “highlight the crucial role vaccines play in larger efforts to prevent COVID-19 infections, which should still include other personal protective measures such as mask-wearing, frequent testing, and social distancing.”

Read more: Experts explain why the mRNA tech that revolutionized COVID-19 vaccines could be the answer to incurable diseases, heart attacks, and even snake bites: ‘The possibilities are endless’

The research, which was funded by the UK government, used the Zoe app, a symptom-tracker with more than 4.7 million users worldwide.

The researchers compared those who said they were vaccinated with either Pfizer, Moderna, or AstraZeneca’s vaccines and those who were unvaccinated. They took into account other factors like age, health risk factors and geographical location that may impact the results.

The symptoms they looked at included: fever, chills, persistent cough, fatigue, shortness of breath, loss of smell, hoarse voice, chest pain, tummy pain, diarrhoea, confusion, eye discomfort, dizziness, sore throat, unusual muscle aches, blisters on feet, worse hayfever, hair loss, and brain fog.

The self-reported nature of the data means that some data was inaccurate or missing. A COVID-19 infection was proven either with a lab test or quicker lateral flow test.

Protection against variants

The study, which took place between December 8, 2020, and July 4,  captured infections caused by both the formerly dominant Alpha variant and the highly infectious Delta variant, which has mutations that help it avoid the immune response. But the variant that the participants caught was not looked at in the study.

Previous real-world studies have shown that Pfizer and AstraZeneca’s vaccines are 88% and 60% effective respectively against COVID-19 with symptoms caused by the Delta variant that’s now most common in most countries worldwide, including the UK and US.

Dr. Sara Oliver, epidemic intelligence service officer at the CDC, said in a presentation on Monday that since Delta appeared, vaccine effectiveness against hospitalization ranged from 75% to 95%. 

In the US, 52.4% of people are fully vaccinated, while in the UK, 64% of Brits are fully vaccinated, according to the Johns Hopkins University.

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Health

Vaccines could prevent asymptomatic infection. Here’s why that’s key to ending the pandemic.

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Vaccine distribution is ramping up in many countries, but with Covid-19 cases also climbing once again and the prospect of another surge of infections on the horizon, the world is in a race against time.

Key to winning the race, experts say, is not only whether the vaccines will play a significant role in preventing serious illness from Covid-19, but also whether they can block people from spreading the virus.

“The ideal vaccine would have two performance features: One prevents you from going to the hospital, going to the ICU and losing your life,” said Dr. Peter Hotez, co-director of the Center for Vaccine Development at Texas Children’s Hospital and dean of the National School of Tropical Medicine at Baylor College of Medicine. “But if the vaccine also halts asymptomatic spread, then you could potentially vaccinate your way out of the epidemic.”

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Early indications have been promising so far. The effect of vaccines on asymptomatic infection had been a big unknown, but scientists say it will be crucial to ending the pandemic.

It’s estimated that asymptomatic cases, which involve people who are infected with Covid-19 but have no symptoms, account for more than half of all transmissions of the virus, according to a recent study published in the journal JAMA Network Open by researchers at the Centers for Disease Control and Prevention. If vaccines can block asymptomatic infections, they could also significantly reduce overall transmission, offering hope that the virus may soon be contained.

Vaccines can protect against transmission by reducing a person’s viral load, or how much virus is present in the body, said Dr. Becky Smith, an associate professor of medicine at Duke University.

“Theoretically, by reducing your viral load, it should prevent your ability to transmit to others,” she said. “And even if it doesn’t fully prevent transmission, it should lower it significantly.”

The focus on vaccines and transmission comes at an important juncture in the pandemic. Although cases globally fell for several weeks, some European countries are now seeing rebounds. Parts of the U.S. are also reporting upticks, a worrisome development given that many states recently relaxed public health restrictions.

Concerns about coronavirus variants, including strains that may be more contagious, also persist. The government’s top infectious disease expert, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told NBC News’ Richard Engel on Thursday that the U.S. needs to vaccinate as many people as possible to avoid further outbreaks.

Part of that strategy hinges on the effect vaccine could have on reducing transmission.

Last week, new data from Israel, where nearly 60 percent of the country’s 9 million residents have received at least one dose of a vaccine, suggested that the Pfizer-BioNTech vaccine is 94 percent effective at preventing asymptomatic infections.

A separate study conducted by researchers at Cambridge University, in the United Kingdom, found that a single dose of the Pfizer vaccine can reduce asymptomatic infections by 75 percent. The results, which have yet to be peer-reviewed, came from an analysis of around 4,400 tests conducted on vaccinated health care workers in Cambridge over a two-week period in January.

In Johnson & Johnson’s trials, the company’s vaccine was found to be 74 percent effective against asymptomatic infections. And according to a report released in December by the Food and Drug Administration, early data suggested that Moderna’s vaccine may also protect against asymptomatic infections, but the company has said more research is needed.

Angela Rasmussen, a virologist at the Georgetown University Center for Global Health Science and Security, said the early findings are “very promising.” But she added that there are still some big unanswered questions.

“From the real-world data that we have so far, it does look like the vaccines have an impact on asymptomatic infection,” she said. “The real question, though, is how broad will this be?”

And because vaccines aren’t 100 percent effective, it’s possible that a small number of vaccinated people could become infected with the virus. If that does happen and a vaccinated individual is asymptomatic, it’s not yet known whether the person could spread Covid-19 to others, Rasmussen said.

In a new commentary published Thursday in the journal Science, Rasmussen and Saskia Popescu, an infectious disease epidemiologist at George Mason University in Virginia, detail why controlling “symptomless transmission” is critical to ending the pandemic. Symptomless transmission includes both people who have no symptoms and those who are pre-symptomatic but later go on to develop symptoms.

“As more people get vaccinated, that will have a population-wide effect on transmission, but while the majority of people right now are not vaccinated, we need to be mindful of the issue of asymptomatic and pre-symptomatic transmission,” Rasmussen said.

Most scientists agree that there are two main paths out of the pandemic. One involves reaching a threshold known as herd immunity — when enough people have developed antibodies from natural infection or from vaccines that future outbreaks are unlikely. The other requires clamping down on the spread of the virus so much that even unvaccinated parts of the population face little risk of becoming infected.

If vaccines can protect against asymptomatic infection, they could help with the latter, but the two strategies shouldn’t be mutually exclusive, Rasmussen said.

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“It’s really a suite of interventions,” she said. “We need to be thinking of ways to get transmission down overall, and we need to not be relying exclusively on the vaccines.”

One way to drive down overall transmission is to heed public health measures that have been in place throughout the pandemic, such as practicing social distancing, wearing masks and avoiding gatherings with unvaccinated people. If the virus can be adequately contained, aspects of life could return more to normal even if parts of a population are still unvaccinated, Rasmussen said.

“We don’t need to be at the herd immunity threshold to relax restrictions,” she said. “If we can get the virus to be so uncommon in the population, there won’t be a risk of people being exposed to it, whether they’re vaccinated or not.”

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Health

Asymptomatic infection blunder let Covid-19 spin out of control

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Jan. 24 marks the one-year anniversary of a momentous but largely unnoticed event in the history of the Covid-19 pandemic: the first published report of an individual infected with the novel coronavirus who never developed symptoms. This early confirmation of asymptomatic infection should have set off alarm bells and profoundly altered our response to the gathering storm. But it did not. One year later we are still paying the price for this catastrophic blunder.

At least one of three people infected with SARS-CoV-2, the virus that causes Covid-19, do not develop symptoms. That’s the conclusion of a review we just published in the Annals of Internal Medicine. It summarizes the results of 61 studies with more than 1.8 million people.

But during much of the pandemic, fierce resistance — and even outright denialism — in acknowledging this not-so-typical disease pattern led to ineffective testing practices that allowed the pandemic to spin out of control.

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On Jan. 28, 2020, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said, “In all the history of respiratory-borne viruses of any type, asymptomatic transmission has never been the driver of outbreaks. … Even if there’s a rare asymptomatic person that might transmit, an epidemic is not driven by asymptomatic carriers.”

This was a widely held view. On June 8, 2020, a senior official of the World Health Organization called asymptomatic transmission “very rare.”

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To his credit, Fauci was among those who immediately criticized this remark. Based on epidemiological data that had become available since his earlier comments, he said it was “not correct” to characterize asymptomatic transmission as rare.

In June, when we published a report of 16 cohorts with sizable proportions of asymptomatic infection and suggested that it might play a role in the progression of the pandemic, several researchers wrote letters to the editor demanding that our paper be retracted.

Today, the best evidence suggests that about half of Covid-19 cases are caused by infected people who do not have symptoms when they pass on the virus. These symptom-free spreaders are roughly divided between those who later develop symptoms, known as pre-symptomatic individuals, and those who never develop symptoms.

While the importance of asymptomatic infection in understanding Covid-19 has been surprising to some, infectious disease experts have long known that infection without symptoms is common in many illnesses. More than 90% of people infected with poliovirus have no symptoms. And about 75% of influenza infections have been estimated to be asymptomatic. Yet these important precedents have largely been ignored.

Asymptomatic coronavirus infection is not necessarily benign. Several studies have reported abnormal lung scans in those infected without symptoms, as well myocarditis, a type of heart inflammation. The long-term health implications of asymptomatic infection aren’t known.

Even though knowledge about asymptomatic infection has greatly evolved, tactics for combating the pandemic have not. It is now obvious that testing only those with symptoms, as was common early in the pandemic, is a mistake because it ignores the invisible legions of infected people who have no symptoms. But it is not enough to merely increase the number of tests. The problem is that current testing practices are ill-suited to detecting and containing asymptomatic infection.

Virtually all of the coronavirus testing performed in the U.S. looks for the genetic material of the virus using the polymerase chain reaction (PCR). It requires expensive equipment and trained technicians. Results are typically returned days — sometimes even weeks — after the test. That means people learn they have been infected with SARS-CoV-2 long after they may have passed the virus to others. Testing becomes more about accounting — tallying the number of detected infections — than about containing the spread of the virus.

What’s needed is a pivot to a different type of testing. Antigen tests, which look for a bit of coronavirus protein, cost just a few dollars each and can yield results in minutes. Like home pregnancy tests, they require minimal instruction. Antigen tests are ideal for spotting people who are infectious, rather than those who may be long past the infectious phase of Covid-19, or who harbor such low levels of the virus that they are unlikely to infect others.

Inexpensive rapid home tests would help infected people isolate themselves before they could spread the virus. Frequent testing — at least several times per week — is essential, as demonstrated by successful testing efforts at some universities, which have enabled students to return to campus. A new focus on self testing, in combination with financial assistance and perhaps even temporary housing for isolation, would directly address the problem of asymptomatic infection.

The rollout of Covid-19 vaccines brings with it the risk of a new wave of asymptomatic infections. The two vaccines authorized by the Food and Drug Administration have been proven to prevent illness, but not asymptomatic infection. Even after vaccination, the coronavirus may still temporarily take up residence in the lining of the respiratory tract, making it possible to infect others. Preliminary results from one vaccine trial seem encouraging, with an apparent two-thirds reduction in asymptomatic infection after the first dose. But many other studies are underway.

There is no time machine that would allow us to return to Jan. 24, 2020, and make the plans we should have made, which would have acknowledged the importance of asymptomatic infection. But it is not too late to recognize the blunder and move aggressively toward testing practices that will help end the pandemic.

Daniel P. Oran is a member of the digital medicine group at Scripps Research Translational Institute, of which Eric J. Topol is founder and director.

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