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  • Experts say the window of highest infectivity seems to occur 2 days prior to symptom onset to 3 days after symptom onset.
  • Rapid antigen tests can detect high viral loads and are currently thought to be reliable in telling people whether or not they could still be contagious.
  • Health officials recommend isolating for at least 5 days if you develop COVID-19 and continuing to wear a mask for up to 10 days whenever you’re in public.

Infectious disease specialists believe that, on average, the vast majority of people who contract the novel coronavirus are most contagious immediately before and immediately after symptoms appear.

Research earlier this year indicated that most people may no longer be contagious 5 to 6 days after symptoms appear. Still, some evidence suggests about one-third of people who contract the infection continue to be infectious for a longer period.

A new study now provides more details on when people may be able to end their isolation.

Researchers in Massachusetts used rapid antigen tests on 40 people beginning on the 6th day after their initial positive COVID-19 test. Of the participants, 36 had received a primary vaccine series and a first booster dose. Most of them were younger and had not been hospitalized for COVID-19.

The researchers reported that 75 percent of the participants still tested positive on day 6. However, only 50 percent of those who tested positive had a “culturable virus.” All of the people who tested negative had a negative viral culture.

The researchers stated that the findings suggest that a person who tests negative after 5 days but still has lingering symptoms may be able to safely end their isolation. They add that a person who tests positive after 5 days but doesn’t have symptoms may be able to safely end their isolation.

In all instances, people who’ve tested positive for COVID-19 are encouraged to wear a mask for up to 10 days whenever they are in public.

Health experts recommend rapid antigen tests over PCR tests because they can detect high viral loads and are thought to be more reliable in telling people whether or not they could still be contagious.

“For a symptomatic infection, the time from illness onset has been shown to be more reliable than PCR testing to predict the presence of live [or] contagious COVID-19 virus,” Dr. Charles Bailey, the medical director for infection prevention with Providence Mission Hospital and Providence St. Joseph Hospital in Orange County, CA, told Healthline.

“Antigen testing may be more capable of determining infectivity since its threshold for detecting COVID-19 more closely aligns with an amount of virus capable of transmission,” he added.

According to Bailey, the length of infectivity will vary from person to person and depends on the severity of infection, the intensity of exposure, and each person’s immune system.

In general, the window of highest infectivity seems to occur 2 days before symptom onset to 3 days after symptom onset.

Contact tracing studies from earlier in the pandemic have found that it’s less common for transmission to occur when exposed to a person 6 days after their symptom onset.

It’s still possible for people to transmit the virus to others after 5 days of symptoms, which is why health officials are advising people who recently recovered from their illness to continue wearing a mask for another 5 days when they’re around other people.

One study published in the International Journal of Infectious Diseases found that about one-third of people with the infection continues to be contagious after 5 days.

But it’s unclear if this remains true with the latest Omicron variants.

A study from Japan found that people with the Omicron variant shed the virus for longer after symptoms appear.

The study suggests that the peak of viral shedding with the Omicron variant may be 2 or 3 days longer than previous variants.

Dr. Julie Parsonnet, an infectious diseases epidemiologist with Stanford Medicine in California, says there doesn’t appear to be a strong relationship between a person’s symptoms and how much virus is in their nose and throat.

But in general, people who’ve tested positive and are symptomatic are more at risk of transmitting and should isolate at home to avoid transmitting the virus to others.

“People whose symptoms are not improving — particularly if they have coughing and sneezing — should continue to stay home until they’re feeling better,” Parsonnet said.

If someone carrying the virus is coughing or sneezing, there’s a greater chance they can spread the virus to others since they’re releasing respiratory droplets that carry the virus.

Researchers are still studying if and how symptoms correlate to how contagious a person is.

“We don’t exactly how symptom duration relates to how long someone is contagious, but we do typically associate symptoms like a fever as an indication that someone is still infectious,” said Dr. John Carlo, the CEO of Prism Health North Texas and member of the Texas Medical Association COVID-19 Task Force.

Research has also shown that people with asymptomatic infections, although less likely than symptomatic individuals to spread the infection, can transmit it to others.

Parsonnet says it’s difficult to quantify how long asymptomatic individuals are contagious because it’s hard to identify when and how long they’ve been infected.

“Asymptomatic transmission might prove to be more common with the Omicron variant given its higher infectivity, but too early to draw this conclusion now,” Bailey said.

There’s no reliable or easy way to determine if you’re still contagious, which is why health officials recommend isolating at home for 5 to 10 days, depending on your symptoms.

Those who are asymptomatic or improving after 5 days are now advised they can end their isolation but continue wearing a mask around other people for another 5 days.

According to guidance from the Centers for Disease Control and Prevention (CDC), those who aren’t improving after 5 days should continue isolating at home until their symptoms improve and fever subsides.

Most infectious diseases doctors do not recommend taking a PCR test to determine if you’re still shedding the virus.

PCR tests are sensitive and can detect non-infectious viruses after infection for up to 90 days.

Many doctors recommend using rapid antigen tests as they pick up on high viral load, which may or may not correlate to how infectious a person is.

“It’s important to remember that COVID-19 tests currently available are not really designed to tell whether or not someone is infectious. They are designed to test whether or not someone has a COVID-19 infection which is slightly different,” Carlo said.