The common perception that almost everyone in America seemed to have acquired the Omicron variant last winter might not be far from the truth. By February 2022, nearly 60% of the population had been infected with the coronavirus, nearly double the proportion seen in December 2021, according to data released Tuesday by the Centers for Disease Control and Prevention.
“In February 2022, the evidence for previous Covid-19 infections increased significantly across all age groups,” said Dr. Kristie Clarke, the agency’s researcher who led the study, during a briefing. press conference.
Infections rose most sharply during the Omicron surge among children and adolescents, possibly because many people in those age groups were still unvaccinated. The increase was smallest in adults aged 65 or older, who have the highest vaccination rate and may be the most likely to take precautions.
The new research suggests that three out of four children and adolescents in the United States had been infected with the coronavirus in February 2022, compared to a third of older adults.
While some studies suggest that prior infection provides a weaker shield against the virus than vaccines, the resulting antibodies should provide a reasonable degree of protection against severe disease, at least in the short term.
“We still don’t know how long infection-induced immunity will last,” Dr. Clarke said.
Population-wide immunity gains may explain why the new wave sweeping China and many countries in Europe has so far been muted in the United States.
The results may offer some comfort to parents who have been anxiously awaiting approval of a vaccine for younger children. Many of these children now appear to have acquired at least some immunity.
Even so, Dr. Clarke urged parents to vaccinate children who qualify as soon as regulators approve a vaccine for them, regardless of any previous infections. She noted that when children are hospitalized with the coronavirus, up to 30% of them may need intensive care.
Many of these children also have other medical conditions. But up to 70% of cases of multisystem inflammatory disease, a rare consequence of Covid-19 infection, occur in children who were otherwise healthy.
“As a pediatrician and a parent, I would absolutely support children being vaccinated, even if they have been infected,” Dr. Clarke said.
Coronavirus cases are rising again in the United States, particularly in the Northeast, but so far the increase in hospitalizations has been minimal and deaths continue to decline.
Even among those who are hospitalized, “we’re seeing less oxygen use, fewer intensive care stays, and thankfully we haven’t seen any increases in deaths associated with them,” said CDC director, the Dr. Rochelle Walensky. “We expect the positive trends to continue.”
CDC researchers began assessing antibody levels in people at 10 sites early in the pandemic and have since expanded that effort to all 50 states, the District of Columbia and Puerto Rico. Investigators use a test that is sensitive enough to identify previously infected people for at least a year or two after their exposure.
The researchers analyzed blood samples taken from September 2021 to February 2022, looking for antibodies against the virus; then they analyzed the data by age, gender and geographic location. The investigators looked specifically for a type of antibody produced after infection, but not in people who had just been vaccinated.
Between September 2021 and December 2021, the prevalence of antibodies in samples steadily increased by one to two percentage points every four weeks. But it jumped sharply after December, rising nearly 25 points in February 2022.
The percentage of samples containing antibodies increased from around 45% to around 75% in children aged 11 and under and adolescents aged 12 to 17.
By February 2022, about 64% of adults aged 18 to 49, about half of those aged 50 to 64 and about a third of older adults had been infected with the virus, according to the study.