The data comes from an ongoing study of blood samples sent to commercial laboratories across the United States.
At the beginning of December, an estimated 34% of Americans had antibodies showing they had once had the virus that causes Covid-19. By the end of February, after a torrent of cases caused by the Omicron variant, that number had jumped to 58%.
“The highest jump in antibody detection was among children and adolescents,” said Dr. Kristi Clark, the pediatrician who led the study for the Centers for Disease Control and Prevention.
By February, nearly 75%, or 3 in 4 children under 18, had developed antibodies to Covid-19, according to the study. The lowest increase was recorded among adults 65 years and older. The CDC estimates that 33% of older adults have contracted Covid-19.
However, it is not clear what these test results mean for personal or community protection against future infections.
“We still don’t know how long immunity from infection will last, and we can’t know from the study, again, whether all people who tested positive for SARS-CoV-2 antibodies continue to be protected from previous infections,” Clark said. Tuesday.
For this reason, the Centers for Disease Control and Prevention says, it remains important for all Americans to stay up to date on Covid-19 vaccines, and get recommended shots and boosters.
However, for people who have been infected within the past three months, Clark says, “you may be able to wait to get your second stimulant dose.”
Estimates were drawn from random, anonymous tests of blood samples sent to commercial laboratories in the United States. The test measures antibodies made against parts of the virus that causes Covid-19; These antibodies are not produced by vaccines, so the test is used to estimate the percentage of the population infected with SARS-CoV-2.
The CDC says the antibodies it measures for the study remain positive for at least two years after infection, so the study should pick up on infections that have occurred since the beginning of the epidemic.
Clark said the CDC does not recommend that people seek antibody testing.
“It’s not something we recommend individually, because it doesn’t change our recommendation in terms of what you should do,” she said, such as keeping up with vaccinations and discussing other preventative measures with your doctor.
The study comes as two new, more infectious variants, BA.2 and BA.2.12.1, dominate transmission in the United States and cause cases and hospitalizations to rise again.
CDC Director Dr. Rochelle Walinsky said Tuesday that the agency is paying close attention to cases of Covid-19 in the Northeast.
“There are some areas in the country, particularly in the northeast, where we’re seeing more cases and we’re starting to see some hospitalizations,” she said.
Walinsky said health officials haven’t seen the numbers increase as much as we were expecting earlier in the pandemic, “thanks, I think, to a great deal of protection in the community” and from vaccines.
“But this is something we need to monitor carefully,” she said.