More than half of Americans have shown previous signs of Covid-19, including three in four children, according to a new report released Tuesday.
The Centers for Disease Control and Prevention (CDC) findings came after researchers examined blood samples from more than 200,000 Americans and looked for virus-fighting antibodies made from infections, not vaccines. They found that signs of previous infection spiked between December and February, when the most infectious type of Omicron spread in the United States.
For Americans of all ages, about 34% had previous signs of infection in December. After just two months, 58% did.
“I was expecting it to increase. I didn’t expect it to increase this much,” said Dr. Christy Clark, co-leader of the CDC team that tracks the spread of coronavirus infection.
In the CDC report, the increase was most striking in children. The percentage of those 17 and under who had the antibodies increased from about 45% in December to about 75% in February.
Older adults were less likely to get infections in the past. That may be because older adults have higher vaccination rates and may be more likely to take other Covid-19 precautions, such as wearing masks and avoiding crowds, Clark said.
Reported cases saw a huge rise in December and January, then fell almost as dramatically as they rose. But daily case numbers have risen again in recent weeks.
The number of cases is believed to be understated, but officials believe the recent increases reflect a real rise in infections. Many Covid-19 infections are mild enough that patients do not seek care or confirmatory lab tests. Centers for Disease Control and Prevention officials say they plan to release a study soon estimating that in recent months there have been three infections for every reported case.
Another recent trend: US health officials say they have seen two weeks of increases in Covid-19 hospital admissions, although the numbers are still relatively low. Hospital admissions were about 1,600 people per day, an increase of 9% in the previous week, the CDC reported.
However, the available evidence provides reason for optimism about how the pandemic will spread, officials have suggested.
“We don’t expect more severe disease from some of these subvariables, but we are actively studying them,” Dr. Rochelle Wallinsky, director of the CDC, said Tuesday.
The study looked for any detectable level of antibodies. It did not distinguish how many people had levels of potentially protective antibodies. Scientists are still trying to understand the role these types of antibodies play in protecting against future exposure to viruses.
Officials continue to urge Americans to get vaccines and boosters, which provide additional protection against Covid-19 for everyone, including those who were previously infected.
The Associated Press contributed reporting.