Half of People With Omicron Don’t Know They’re Infected, Study Says

More than half of people—56%—who are infected with the Omicron variant are not aware of their infection.

That’s the conclusion of a small study published on Aug. 17 in JAMA Network Open. It’s good news, in some ways, since it underscores the fact that Omicron tends to cause relatively mild symptoms (or no symptoms at all) in vaccinated people. The downside is that many people are likely spreading the virus unintentionally.

Dr. Susan Cheng, director of the Institute for Research on Healthy Aging at the Cedars-Sinai Smidt Heart Institute, and her colleagues at the University of California, Los Angeles and Abbott Laboratories, studied 210 employees and patients at Cedars-Sinai who provided at least two blood samples for antibody testing—one before the Omicron surge and one after. The researchers analyzed them for levels of antibodies to the SARS-CoV-2 virus.

Most of the people in the study were vaccinated, and the researchers measured levels of two different types of antibodies: those that the immune system made in response to the vaccines, and those that the immune system made after infection with the virus. At the start of the study, all of the volunteers had to have infection-induced antibody levels below a certain threshold, indicating they had not recently been infected with the virus. That way, any rise in antibody levels served as a proxy for an infection. The participants also filled out health surveys describing their symptoms and any COVID-19 PCR testing to determine if they had an infection during the study period.

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The researchers found that 56% of the people in the study who tested positive were not aware that they had been infected, either because they did not experience any symptoms of COVID-19 or felt only mild symptoms they attributed to a cold or allergies. The findings support early data from around the world suggesting that throughout the pandemic, anywhere from 25% to 40% of SARS-CoV-2 infections have been asymptomatic, which presents challenges for public-health officials trying to control the spread of the virus.

“If one message comes out of our study, I hope it’s that awareness of your infection status is going to be really key to get us through this pandemic faster,” says Cheng. “Lack of awareness and lack of knowing could lead to walking around with something transmissible, and unwittingly passing the virus to a household member, neighbor, co-worker, or someone at the grocery store.”

The data showed that people’s awareness of their infection status improved after at-home rapid test kits became widely available earlier in 2022. While about 75% of people were unaware of their infection in January and February, only about 56% were by May.

The fact that one out of two people infected with Omicron aren’t even aware that they have COVID-19 makes a strong case for more frequent testing. Regularly testing yourself with at-home rapid antigen kits is a good idea even if you don’t feel sick, since transportation, work, school, and crowded public venues—like for concerts or sports games—are all places where you can potentially get infected.

Knowing your infection status, says Cheng, could become increasingly important as studies show that people are getting infected not just once, but twice and even multiple times with Omicron subvariants. She is currently studying reinfection to better understand how many times people are getting multiple infections, and what risk factors make it more likely.

“Increasing people’s awareness of their status is our goal,” she says. “Unfortunately, we have to live with this virus for some time, and if we can be more aware, then we can potentially help ourselves, our families, and our communities to curb the spread of the virus.”