Even if lots of children have had Covid, they’ll still benefit from the vaccine, experts say

A startling statistic emerged as advisers to the Food and Drug Administration debated use of the Pfizer-BioNTech Covid-19 vaccine in ages 5 to 11 last week. According to one federal scientist, by June an estimated 42 percent of these children had already been infected with the coronavirus.

That figure was much higher than anyone expected. But the estimate, from the Centers for Disease Control and Prevention, might have overstated the percentage of children who were infected, several experts said in interviews. Among other flaws, the percentage was based on tests known to have a high rate of “false positives” — signaling the presence of antibodies where there were none.