These findings add to a growing body of evidence that undiagnosed infections are increasing virus transmission. “A low level of infection awareness has likely contributed to the fast spread of omicron,” said Sandy Y. Joung, an investigator at Cedars-Sinai and the first author of the study, in a news release.
Antibody Tests Found Evidence of Omicron Infection
The study included more than 2,000 Cedars-Sinai healthcare workers and patients. All took two or more blood tests to look for evidence of COVID-fighting antibodies. The first tests were conducted after the delta variant surge (September 15, 2021), and the second after the start of the omicron variant surge (between December 15, 2021, and May 4, 2022). The researchers found that 210 study participants had evidence of infection during the omicron wave, as shown by newly positive levels of antibodies to SARS-CoV-2, the virus that causes COVID-19. Next, participants were invited to complete a health survey that included questions about recent vaccinations, symptoms, and other changes in their health. Everyone was specifically asked whether or not they had developed any new known infections since completing the previous health update or study visit. Researchers found that only 44 percent of study participants with newly positive SARS-CoV-2 antibodies knew they had COVID-19. The majority — 56 percent — were unaware. Of the participants who were unaware they’d had COVID-19, only 1 in 10 reported having any recent symptoms, which they attributed to a common cold or other type of infection.
Omicron Can Cause Mild or No Symptoms for Many People — but Not All
The study findings are a reminder that omicron is not only stealthy but also highly variable in how it affects different people, says Susan Cheng, MD, MPH, a coauthor of the study and the director of the Institute for Research on Health Aging in the Department of Cardiology at Cedars-Sinai. “As we know, the generally milder version of COVID caused by omicron leads to cold-like symptoms, and most people recover at home. However, a significant number of people can become severely ill, need hospitalization, or even die from omicron, and we are still not very good at predicting exactly who the more vulnerable people are,” says Dr. Cheng. While there is a spectrum of illness with COVID-19, people increasingly have some level of immunity from vaccination, prior infection, or a combination of both, says Amesh A. Adalja, MD , a senior scholar at the Johns Hopkins Center for Health Security in Baltimore, who was not involved in the study. This has caused asymptomatic infections or ones with very mild symptoms to become more common, he adds.
When in Doubt, Lie Low and Take a COVID-19 Test
Cheng advises anyone who feels their health is a bit off to take it easy, monitor symptoms, and test themselves for COVID-19. “Two rapid tests done over the span of a couple of days after symptoms have started will offer some sensitivity, but are not going to be 100 percent accurate,” she says. “Sensitivity” measures how often a test correctly delivers a positive result for people with the condition that’s being tested. Adalja agrees, saying that anyone with symptoms that could be COVID-19 — even if minor — should get tested. Limiting your contact with other people will also help prevent the spread of anything that may or may not be COVID-19. “If I’ve been exposed, I will decide to lie low for a while, watch for symptoms, be extra cautious with where I go and whom I’m in contact with, wear a good quality mask as needed, and also take extra care of my health, which often means trying to get some extra sleep,” says Cheng.
Should You Get an Antibody Test to Find Out if You’ve Had COVID-19?
You may be tempted to get an antibody test because you’re curious about whether you ever unknowingly had COVID-19 — and, if so, if you have antibodies that will help protect you against reinfection. Although previous COVID-19 infection provides some extra immunity, that window of protection has gotten significantly smaller with the emergence of omicron. In a study completed in February 2022 that has not yet been peer-reviewed, investigators found that some people caught BA.2, a variant of omicron, as soon as 20 days after they got infected with the original omicron. Antibody tests require a blood draw, and results typically take about 24 hours. Many labs and pharmacies offer antibody testing; ask your doctor or call your local pharmacy if you need help finding one. If your doctor orders an antibody test for you for medical reasons, it may be covered (or mostly covered) by your insurance. At Atrium Health in Winston-Salem, North Carolina, an antibody test costs $80 if insurance doesn’t cover it.
Should You Worry About Long COVID After an Undetected Omicron Infection?
“There are ongoing studies being done to understand the extent to which people who develop even milder forms of omicron infection could go on to develop long COVID or other downstream health issues,” says Cheng. “We don’t yet have all the data on what this could look like,” she adds. On a positive note, it appears that omicron poses less risk of long COVID than delta. A study published in June in the Lancet found that participants’ chance of getting long COVID from omicron was 4.4 percent, compared with almost 10.8 percent from delta. Should a person take an antibody test if they have symptoms that could be long COVID but don’t know if they were ever infected? There’s no simple answer to that, says Cheng. “In some cases, yes, a certain type of antibody testing — if it is the type that can help distinguish between the effects of prior vaccine versus prior natural infection — could help to indicate if there had been a recent prior infection,” she says. But in some cases, the information from even this type of testing may not be helpful because antibodies to infection all tend to wane over time, says Cheng. “And so, if a long time has passed since a prior infection, then the currently available antibody tests unfortunately won’t offer much helpful information,” she says.
