Almost sixty percent of Americans had contracted Covid-19 by February 2022, including about 75 percent of kids, according to a new Centers for Disease Control and Prevention report released Tuesday.
Researchers tested blood samples every four weeks from September 2021 to February 2022 for anti-nucleocapsid (anti-N) antibodies, which are produced after a Covid-19 infection, but not after a vaccination. Last December, just as the Omicron variant began spreading, seroprevalence—the percentage of the population that had antibodies—was at 34 percent of all Americans and about 45 percent of kids under 17. Those numbers increased significantly by February.
“I did expect it to increase. I did not expect it to increase quite this much,” Dr. Kristie Clarke, lead author of the study, said in a media briefing on Tuesday. “This is why we want to get this message out to the U.S. population as soon as possible. This is the first time that population seroprevalence is over 50 percent.”
Researchers found more of an increase in seroprevalence in age groups with the lowest vaccination rate, Clarke said. Adults 65 and older had less of an increase, from about 19 to 33 percent by February, which may be because of higher vaccination rates, but also because they are more likely to take other preventative measures, she explained.
The high number of cases may mean a shift in future infections—severe illness and death might become rarer while milder infections become more common, Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York, tells Apoorva Mandavilli of the New York Times.
“It will be more and more difficult for the virus to do serious damage,” he tells the publication.
But health officials still don’t know how long immunity will last for those who were infected with the virus, Clark said in the briefing.
“We cannot know from the study, again, whether all the people who tested positive for SARS-CoV-2 antibodies continue to have protection from their prior infection,” she said. “What we do know is that vaccination is a safe and effective way to get robust immune protection for a specific amount of time.”
The CDC continues to advise people to get their vaccine and stay up-to-date on booster shots.
“Betting that you are in the 60 percent is a big gamble,” Tom Inglesby, director of the Center for Health Security at the Johns Hopkins Bloomberg School of Public Health, tells the New York Times. “For anyone who’s not been vaccinated and boosted, I would take this new data as a direct message to get that done or expect that the virus is likely to catch up to you if it hasn’t already.”