More than half of Americans show signs of a previous Covid-19 infection, including three out of every four children, according to a new report released on Tuesday.
The findings from the Centers for Disease Control and Prevention (CDC) come 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 past infection rose dramatically between December and February, when the more contagious Omicron variant surged through the US.
For Americans of all ages, about 34% had signs of prior infection in December. Just two months later, 58% did.
“I did expect it to increase. I did not expect it to increase quite this much,” said Dr Kristie Clarke, co-leader of a CDC team that tracks the extent of coronavirus infections.
In the CDC report, the most striking increase was in children. The percentage of those 17 and under with antibodies rose from about 45% in December to about 75% in February.
The older people were, the less likely they had evidence of past infections. That may be because older adults have higher vaccination rates and they may be more likely to take other Covid-19 precautions, such as wearing masks and avoiding crowds, Clarke said.
Reported cases had a huge surge in December and January, then fell almost as dramatically as they had risen. But daily case counts have been trending up again in recent weeks.
The case numbers are believed to be an undercount, but officials do think recent increases reflect a true rise in infections. Many Covid-19 infections are mild enough that patients do not seek care or confirmatory lab tests. CDC officials say they plan to release a study soon that estimates that in recent months there were three infections for every reported case.
Another recent trend: US health officials say they have seen two weeks of increases in Covid-19 hospitalizations, though the numbers remain relatively low. Hospital admissions number about 1,600 per day, a 9% increase in the prior week, the CDC reported.
Available evidence nevertheless offers reason to be hopeful about how the pandemic is going, officials suggested.
“We are not anticipating more severe disease from some of these subvariants, but we are actively studying them,” said Dr Rochelle Walensky, CDC director, on Tuesday.
The study looked for any detectable level of antibodies; it did not distinguish how many people had antibody levels that might be protective. Scientists are still trying to understand what role these kinds of antibodies play in protection from future virus exposures.
Officials continue to urge Americans to get vaccines and boosters, which offer additional protection against Covid-19 for all, including those who were previously infected.
The Associated Press contributed reporting.