By February of this year, 58 percent of the US population -- or more than 190 million people -- had been infected with Covid, according to an antibody survey carried out by the Centers for Disease Control and Prevention (CDC) published Tuesday.
The figure is far higher than the 80 million officially recorded cases, with the majority of infections undiagnosed, asymptomatic or unreported.
Roughly 75 percent of people under 18 had been infected, according to a paper based on a nationally representative study of antibody levels.
There was a huge surge during last winter's Omicron wave, particularly among children.
Each month from September 2021 to January 2022, the study examined some 75,000 blood specimens across the country, as well as 45,000 samples in February.
The study examined only antibodies created in response to prior infection, not vaccination.
National estimates were then produced using statistical methods to weight by age, sex and metropolitan status.
"Having infection-induced antibodies does not necessarily mean you are protected against future infections," said Kristie Clarke, co-lead for the national Covid-19 serology task force, on a call with reporters.
"Previous infection has been shown to provide some protection against severe disease and hospitalization -- and vaccination, either before or after infection, provides additional protection," she added.
Since the duration of infection-conferred immunity is unknown, it remains vital to stay up to date with Covid vaccination, she stressed.
The United States is currently offering fourth shots to people 50 and over, and third shots to people under that age.
Children five and under are the only group not yet eligible for vaccination.
Nationwide, cases are ticking up with infections caused by the BA.2 and BA.2.12.1 Omicron subvariants.
Upstate New York and the Northeast region are also experiencing an increase in hospitalizations, and the CDC recommends indoor masking in those areas, though mandates have long ceased to be in effect there.
Even with rising hospitalizations, the number of deaths is continuing to fall, and currently stands at a little over 300 per day. The country is expected to reach the grim milestone of one million deaths in the coming weeks.