NEW YORK (AP) — Three out of four American children have been infected with the coronavirus and more than half of all Americans had signs of previous infections, researchers from the Centers for Disease Control and Prevention estimated in a report Tuesday. Tuesday.
The researchers examined blood samples from more than 200,000 Americans and looked for antibodies that fight the virus from infections, not vaccines. They found that signs of past infection increased dramatically between December and February, when the most contagious omicron variant emerged in the US.
For Americans of all ages, about 34% had signs of prior infection in December. Just two months later, 58% did.
“I expected it to increase. I didn’t expect it to get that high,” said Dr. Kristie Clarke, co-leader of a CDC team tracking the extent of coronavirus infections.
The news came as Pfizer applied for permission to offer a booster dose to children ages 5 to 11, as well as people over the age of 12.
In the CDC report, the most striking increase was in children. The percentage of those under 17 with antibodies increased from around 45% in December to around 75% in February.
The older people were, the less likely they were to have evidence of past infections. That may be because older adults have higher vaccination rates and are more likely to take other precautions against COVID-19, such as wearing masks and avoiding crowds, Clarke said.
Reported cases of COVID-19 had a big spike in December and January, then fell almost as dramatically as they had risen. But daily case counts have been rising again in recent weeks.
The number of cases is believed to be an undercount, but authorities believe the recent increases reflect a true rise in infections. Many COVID-19 infections are mild enough that patients do not seek care or confirmatory laboratory tests. CDC officials say they plan to release a study soon that estimates there have been three infections for every reported case in recent months.
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 are about 1,600 a day, a 9% increase from the previous week, the CDC reported.
However, the available evidence offers reason to be hopeful about how the pandemic is faring, officials suggested.
“We are not anticipating more severe disease from some of these subvariants, but we are actively studying them,” CDC Director Dr. Rochelle Walensky said Tuesday.
Tests that showed how many people had previous infections can detect antibodies for a year or two after infection, and possibly longer. Studies have shown that a prior infection can protect some people from serious illness and hospitalization, but CDC officials stressed that previously infected people should still be vaccinated against COVID-19.
The study looked for any detectable level of antibodies; it did not distinguish how many people had levels of antibodies that might be protective. Scientists are still trying to understand what role these types of antibodies play in protecting against future virus exposures.
Officials continue to urge Americans to get vaccinated and booster shots, which offer additional protection against COVID-19 for everyone, including those who were already infected.
Currently, the US offers a booster dose starting at age 12, but Pfizer and BioNTech asked the Food and Drug Administration (FDA) on Tuesday to allow healthy children of primary school also received one, about six months after their last injection. The companies cited a small study showing that the extra injection for children ages 5 to 11 revved up antibodies capable of fighting off the super-contagious omicron variant. Pfizer children’s injections are one-third the dose given to anyone 12 years and older.
AP Medical Writer Lauran Neergaard in Washington contributed to this report.
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