Covid-19 Can Leave You Infectious After Five or Even 10 Days

CDC recommends at least five days of isolation, but some people are testing positive well past that

Authors: Brianna Abbott May 31, 2022 The Wall Street Journal

Seeing that bright red line appear on an at-home Covid-19 test can feel inevitable during a surge like the one under way now. What can be surprising is how many days later that line keeps popping up.

The Centers for Disease Control and Prevention recommends five days from first symptoms or diagnosis as a minimum isolation period before infected people can return to public activities while maintaining certain precautions. Yet some people continue to test positive for the Covid-19 virus on rapid tests beyond those five days. Some even test positive after 10 days and after symptoms have resolved.

The question then becomes: How long are people infectious? Into the pandemic’s third year, as new, more infectious variants continue to circulate widely and more people have built-up immune defenses, researchers aren’t totally sure when or how long individuals with Covid-19 might be contagious and shedding virus, particularly at the end of an infectio

“It’s still up for debate,” said Nathaniel Hafer, director of operations for the University of Massachusetts Center for Clinical and Translational Science.

The isolation guidance that the CDC updated amid Omicron’s rapid spread is likely leading some people to leave isolation while they are contagious, some health experts and clinicians said, particularly if people don’t wait for a negative rapid test and aren’t wearing high-quality masks for a full 10 days.

“We know that people will be returning to work while they’re still infectious, even if they feel better,” said Carina Marquez, an associate professor and infectious-disease doctor at the University of California, San Francisco.

Dr. Marquez said she tested positive on an at-home test for 13 days recently, a period when she decided to work remotely. For those without that option, Dr. Marquez said that they should stop isolating after getting a negative rapid test, or they should stop isolating after 10 days and wear a mask, whichever comes first.

The CDC recommends that everyone wear a well-fitted mask and avoid travel and being around high-risk people for 10 days, no matter when the person leaves isolation.

The CDC didn’t immediately comment on its guidance.

No test can perfectly tell whether someone with Covid-19 is contagious, infectious-disease experts and laboratorians said. A more accurate indicator is culturable virus, a test of whether a virus sample taken from a patient can infect cells in a lab. But such tests are complex and can only be run in labs with certain safety protocols.

Several studies suggest that positive results on rapid antigen tests such as the iHealth, QuickVue and BinaxNow often match with culturable virus results. Some public-health experts have encouraged people to use at-home tests as a gauge for infectiousness, especially since they have become more widely available.

The tests often only turn positive when a person is carrying large amounts of virus. At the beginning of an infection, when a person’s viral load is rising, it might take a few days before tests turn positive. That is why health authorities recommend that people with symptoms and negative rapid-test results wait and retest or get a more sensitive lab-based PCR test.

As a person’s viral load drops, rapid tests are a better indicator of who is no longer infectious, public-health experts said. The University of Chicago started deploying the tests in December to figure out which healthcare workers could safely come back to work and help alleviate staffing shortages before 10 days of isolation, said Emily Landon, U Chicago Medicine’s executive medical director of infection prevention and control.

More than 40% of 260 healthcare workers who felt well enough to work were positive the first time they took a rapid test between days five and 10 of an infection, Dr. Landon and her colleagues found, according to a preprint study that isn’t peer-reviewed.

“We didn’t feel comfortable having them come back,” Dr. Landon said.

The CDC has said data shows that most transmission occurs early in the course of infection and that peak infectiousness declines within a week of symptom onset. Much of that data was gathered before the emergence of an Omicron variant much more infectious than those that preceded it.

More recent studies have demonstrated that a significant portion of people test positive on rapid tests after five days, including one published by the CDC in February that found 54% of people had positive rapid-test results between days five and nine after symptoms or diagnosis. The percentage of positive results declined over time. The authors wrote that the evidence reinforced the importance of mask use during that period and that rapid tests could be a useful tool for guiding isolation recommendations.

One recent study found that only 17% of vaccinated college students had culturable virus beyond day five, while a separate study of people with mild Covid-19 cases found more than 50% had culturable virus at day five and 25% did at day eight. Neither study has been peer-reviewed.

“It does make us concerned that people are still able to transmit at day five or day eight,” said Amy Barczak, an infectious-disease doctor at Massachusetts General Hospital in Boston and senior author of one of the studies.

Both studies found that a negative rapid test after an initial diagnosis is a good indicator that a person no longer has culturable virus and a solid sign they are likely no longer contagious. With a positive rapid-test result toward the tail end of the 10 days, however, it can be more difficult to tell how infectious that person might be, especially if they are feeling better and the line is growing fainter.

“You should consider yourself potentially having transmissible virus,” said Tara Bouton, an assistant professor of medicine at Boston University School of Medicine and lead author on another one of the studies. People who stop isolating before 10 days should wear a high-quality mask like an N95 and keep contacts to a minimum, Dr. Bouton said.

Immunocompromised people and those who get severely ill can be contagious even longer, studies suggest, and patients who experience rebounding symptoms or who test positive again after taking Pfizer Inc.’s Paxlovid pill should also assume that they are contagious, infectious-disease experts said.

Generally, studies suggest it is rare for virus to be culturable after 10 days. Infectious-disease experts disagree about whether most people should continue to test beyond that point.

“These tests aren’t perfect,” U Chicago’s Dr. Landon said. “They underestimate contagiousness in the beginning of illness and overestimate at the end…but not by that much.”

Were fears about asymptomatic Covid spread overblown? 

Infected people without symptoms are TWO-THIRDS less likely to pass virus on, study finds

Authors: JOHN ELY MAILONLINE 26 May 2022 

Fears about silent spreaders of Covid — who suffer no symptoms but can pass the virus to others — may have been overblown. 

A study of nearly 30,000 people has found asymptomatic carriers are about 68 per cent less likely to pass the virus on than those who get sick.  

No10 used concerns about asymptomatic spread to justify forcing Britons to obey lockdowns and wear masks.  

They were thought to account for up to a third of all infections and many scientists claimed asymptomatic patients were just as infectious as the sick.

But a new global study spanning 42 countries, including the UK and US, found they were only responsible for as little as 14 per cent of cases. 

They also estimate that their overall risk of passing the virus to someone else ‘about two-thirds lower’. 

Scientists claimed Covid’s ability to spread asymptomatically was one of the reasons for harsh social curbs.

During one of the national lockdowns in January 2021, the Government said about a third of people with Covid had no symptoms and urged people to ‘act like you’ve got it’.

Experts analysed data from 130 studies from 42 countries.

They involved 28,426 people who caught Covid between April 2020 and July 2021. 

Of these patients, nearly 12,000 had an asymptomatic infection, having tested positive on a PCR but having suffered no symptoms. 

All of the studies included the results of community screening programmes, contact tracing, and investigations into specific outbreaks like on cruise ships. 

They found the ‘secondary attack rate’, how likely people infected with Covid are to pass the virus to others, was 68 per cent lower for asymptomatic cases, compared to those with symptoms. 

Scientists also estimated between 14-to-50 per cent of the Covid infections were asymptomatic. 

They said the range was so high due to the differences in the methodologies of the studies they drew the data from. 

But lead author, Diana Buitrago-Garcia, from the University of Bern in Switzerland, suggested their role in overall Covid transmission was minor.  

‘If both the proportion and transmissibility of asymptomatic infection are relatively low, people with asymptomatic SARS-CoV-2 infection should account for a smaller proportion of overall transmission than presymptomatic individuals,’ she said. 

Co-author, Professor Nicola Low, an expert in social and preventative medicine at Bern, said while it was clear asymptomatic cases were less infectious, the true scale of these cases in the pandemic was difficult to calculate. 

‘The true proportion of SARS-CoV-2 infection is still not known, and it would be misleading to rely on a single number because the 130 studies that we reviewed were so different,’ she said. 

‘People with truly asymptomatic infection are, however, less infectious than those with symptomatic infection.’ 

Another limitation of the study, which is ongoing as more data becomes available, is that it only includes studies up to July 2021.

This, as the authors highlight, means it will not include any data on more recent Covid variants like Omicron, which only emerged in November last year and is milder than earlier versions of the virus. 

It also means the sample size includes data from both before and when vaccines were starting to be rolled out in various countries, which could influence the results. 

Most of the studies included in the research, which has been published in the journal PLOS Medicine, were from Europe and the Americas, with 45 from each.  

The authors also highlighted reduced routine testing as countries, like the UK, wind down their routine pandemic testing will also impact future research into asymptomatic cases.

Fears about asymptomatic Covid cases unwittingly spreading the virus were part of a Government rationale for urging people at the start of 2021 to take a test twice a week.

At the time then-Health Secretary Matt Hancock said regular testing was one the best ways to catch asymptomatic cases and keep people safe. 

‘Around 1 in 3 people have coronavirus without any symptoms, so getting tested regularly is one of the simplest and easiest ways we can keep ourselves and our loved ones safe,’ he said. 

‘I’d encourage everyone to take up the offer and test twice a week.’ 

Covid symptoms themselves have undergone several changes over the course of the pandemic.

In the beginning UK health officials only accepted three symptoms: a high temperature, a cough and a loss or change to taste or smell as signs someone had the virus, despite other countries including up to 14.

But in April this year the NHS quietly expanded the list to 12, including a loss of appetite, feeling or being sick and a headache, shortness of breath, feeling tired, an aching body, a sore throat, a blocked or runny nose and diarrhea. 


According to the NHS, symptoms of Covid in adults can include: 

  • a high temperature or shivering (chills) – a high temperature means you feel hot to touch on your chest or back (you do not need to measure your temperature) 
  • a new, continuous cough – this means coughing a lot for more than an hour, or 3 or more coughing episodes in 24 hours 
  • a loss or change to your sense of smell or taste 
  • shortness of breath 
  • feeling tired or exhausted
  • an aching body 
  • a headache 
  • a sore throat 
  • a blocked or runny nose 
  • loss of appetite 
  • diarrhea 
  • feeling sick or being sick