The Food and Drug Administration now recommends that people who have been exposed to the coronavirus should have three negative at-home tests, even if they don’t have symptoms.
The FDA made the change Thursday based on evidence that people with an omicron infection — but who are asymptomatic — need multiple negative rapid antigen tests over a number of days to be sure they don’t have Covid. Rapid at-home tests are more likely to give a false negative result in asymptomatic cases.
“If repeat testing is not performed after a negative result, an infection may be missed and people may unknowingly spread the SARS-CoV-2 virus to others, especially if they are not experiencing symptoms,” the FDA tweeted.
The FDA previously advised serial testing — two times over three days — for asymptomatic people using an at-home Covid test. With the new guidance, the FDA is saying that people who have been exposed to Covid aren’t in the clear after just one or two rapid tests, even if they don’t have noticeable symptoms. It’s especially important before being around other people.
“If you are going to an event, the only test that matters is the test you take right before,” said Michael Mina, chief science officer for the biotech software company eMed. “Even if you have taken three negative tests within 48 hours, if you have been exposed, you should test right before you see people or go to an event to avoid transmission.”
If you’ve been around someone who tested positive, the Centers for Disease Control and Prevention recommends testing immediately if you have symptoms or five full days after exposure.
How many people with Covid don’t have symptoms?
What experts know about asymptomatic Covid is largely based on data collected during previous waves of the virus, when the omicron variants had not yet evolved and the number of people with previous immunity was low. As many as one-third of Covid infections may be spread by people who don’t have any symptoms, early Covid data suggested.
Truly asymptomatic cases are now likely very rare, Mina said.
“In general, asymptomatic cases have gone down,” Mina said, since previous immunity typically triggers an immune response and the mild symptoms that go with it, such as headache, fever and runny nose, even if a person never gets really sick.
With the rapid rise of the BA.5 version of omicron, it’s become more difficult to track asymptomatic cases. Almost 95% of people in the U.S. have some level of immunity, either from vaccination or prior infection, according to the Centers for Disease Control and Prevention. That gives a high level of protection against severe illness, said Dr. Robert C. Bollinger, an infectious disease expert at the Johns Hopkins University School of Medicine.
“If you have a subsequent case, you may not notice because your symptoms are so mild,” Bollinger said.
A South African study published in March did find that the first omicron variants appeared to cause more asymptomatic infections. However, the study did not include the BA.4 and BA.5 omicron subvariants that now make up most of the Covid infections in the U.S.
Covid can spread without symptoms
As the pandemic wears on, people should expect milder symptoms, in general, said Dr. Dean Blumberg, chief of infectious diseases at the University of California-Davis Health.
However, there may be future variants that suppress the immune system or invade cells or replicate faster, ensuring that the human body does not fight off the infection as well and causing more severe symptoms.
“There’s no way we can predict anything at this point. We’ve been so surprised so many times by things that have differed from our expectations. There’s still a lot that we need to learn about Covid,” Blumberg said.
Knowing the proportion of asymptomatic cases can help predict where the pandemic is going, said Dr. Rebecca Fischer, an assistant professor in the department of epidemiology and biostatistics at the Texas A&M University School of Public Health.
“It’s worthwhile to have insight into the frequency of asymptomatic infections to understand the burden of Covid at a given time and to gauge how patterns in asymptomatic, mild and moderate illness change over time, including from variant to variant,” said Fischer, who is principal investigator for university’s Prevent Covid U study.
A CDC spokesperson told NBC News that the agency is conducting ongoing studies to track asymptomatic cases of Covid, including those caused by the omicron variant. The data is not yet publicly available.