More than half of people who were likely infected with the COVID-19 Omicron variant last fall didn’t know they had the virus, which could be why it spread so fast, a new study finds.
The study, done by researchers at Cedars-Sinai hospital in California, is in line with other research showing that at least 25% — and up to 80% — of people infected with COVID-19 don’t show symptoms.
"Our study findings add to evidence that undiagnosed infections can increase transmission of the virus," Sandy Y. Joung, an investigator at Cedars-Sinai and an author of the study, said in a news release. "A low level of infection awareness has likely contributed to the fast spread of Omicron."
Researchers were able to examine blood samples from 2,479 health care workers and patients in the fall of 2021, just before the Omicron wave began. Of those, 210 were likely infected with Omicron based on their antibody levels.
Through surveys and interviews, researchers found that 44% of the 210 people knew they were infected. Of the 56% of people who were unaware, 10% said they had symptoms they attributed to a common cold or other illness.
Investigators said more studies are needed to learn more about what contributes to a lack of infection awareness, but the current study can help people better understand their own risks.
"We hope people will read these findings and think, ‘I was just at a gathering where someone tested positive,’ or, ‘I just started to feel a little under the weather. Maybe I should get a quick test.’ The better we understand our own risks, the better we will be at protecting the health of the public as well as ourselves," Dr. Susan Cheng, the Erika J. Glazer Chair in Women's Cardiovascular Health and Population Science at Cedars-Sinai, said.
Last week, the U.S. Centers for Disease Control and Prevention relaxed its COVID-19 guidelines, dropping the recommendation that Americans quarantine themselves if they come into close contact with an infected person.
The CDC also said people no longer need to stay at least 6 feet away from others.
The changes are driven by a recognition that — more than 2 1/2 years since the start of the pandemic — an estimated 95% of Americans 16 and older have acquired some level of immunity, either from being vaccinated or infected.