On the flip side, the CDC estimated 77.5 percent of people had antibodies from at least one prior infection.
The agency found that by the end of the year, 96.7 percent of Americans had antibodies either from getting vaccinated, getting infected or some combination of the two.
The infection and vaccination stats were often cited by federal health officials when discussing updated recommendations and the loosening of restrictions, most notably the end of the country’s public health emergency earlier this spring.
Still, officials have stressed that the presence of antibodies from a prior infection does not mean a person is permanently protected from the virus. Immunity wanes over time, especially among those without so-called “hybrid” immunity from both an infection and vaccination.
The data was based on seroprevalence — the percentage of individuals who have antibodies in their blood. Both vaccines and infection result in production of anti-spike (anti-S) antibodies, but only infection results in the production of anti-N antibodies, CDC said.
Of all age groups, those 65 and older had the smallest share of hybrid immunity, at less than 93 percent— they also had the smallest share of Americans with at least one prior infection, at 56.5 percent.
Past studies have noted the fact that vaccine coverage for this group is generally higher than the broader population. Additionally, the shots were available much earlier than for the general population, and their behavior was different.
The lower rate of hybrid immunity could mean those people are at further risk of severe infections if they don’t stay up to date with vaccines.
