When are you most likely to spread COVID? Study says initial days are crucial
If you test positive for the coronavirus, try to avoid close contact with others two days before and three days after your symptoms appear, a new study says — that’s when you’re most contagious, although complete isolation is ideal until you test negative.
You can still catch the coronavirus even if you’re around an infected person who doesn’t have symptoms. You’re just more likely to be free of symptoms as well, according to the study published Monday in the journal JAMA Internal Medicine.
The findings underscore the importance of proper isolation when sick, especially in the early days of infection, as well as vaccination, which can reduce the likelihood of developing severe symptoms that can increase your chances of spreading the virus.
“Our results suggest that the timing of exposure relative to primary-case symptoms is important for transmission,” co-lead author of the study Dr. Leonardo Martinez, an assistant professor of epidemiology at the Boston University School of Public Health, said in a statement. “This understanding provides further evidence that rapid testing and quarantine after someone is feeling sick is a critical step to control the epidemic.”
Past research has focused on viral load, or the amount of virus in someone’s upper airways, as an indicator of how likely a person is to spread the coronavirus to others. But the Boston team wanted to confirm what other studies have found by following close contacts of infected people.
Researchers identified about 9,000 close contacts — defined as roommates, co-workers, people in hospital settings and riders in shared vehicles — of infected people in China from January to August 2020.
The team monitored infected people for at least 90 days after testing positive to confirm the presence or absence of symptoms; 89% of people developed mild to moderate symptoms and 11% didn’t have any symptoms.
People who lived with an infected person, who were exposed to the infected multiple times, or were around infected people for long periods of time had higher infection rates than other close contacts, the study found.
Still, close contacts had a greater likelihood of catching the virus if they were exposed to it two days before or three days after symptoms appeared in the infected individual.
It’s important to note the study was conducted on people who contracted the coronavirus before more contagious variants emerged. The dominant version of the coronavirus spreading in the U.S. — the delta variant — is said to be more transmissible and may cause more severe disease, though its virulence is difficult to confirm.
A separate but related study published in November found that people are most contagious during the first five days of their coronavirus infection, when viral load peaks.
This story was originally published August 26, 2021 at 11:25 AM with the headline "When are you most likely to spread COVID? Study says initial days are crucial."
