Experts urge immunizing kids against virus

A startling statistic emerged as advisers to the Food and Drug Administration late last month debated use of the Pfizer COVID19 vaccine in children ages 5 to 11. According to one federal scientist, by June an estimated 42% of these children had already been infected with the coronavirus.

But the estimate, which was from the Centers for Disease Control and Prevention, might have overstated the percentage of children who were infected, several experts said. 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 are none.

And even if unexpectedly high numbers of children have been infected, parents should not assume that they are shielded from the virus and don’t need the vaccine. Immunization will cement that protection now and against future virus variants, said Scott Hensley, an immunologist at the University of Pennsylvania.

Are 42% of younger children really immune to the coronavirus?

Most likely, no. The CDC estimate was based on tests of a small number of children who had blood drawn for routine medical care or other illnesses. That is not a representative sample of the general population, said Akiko Iwasaki, an immunologist at Yale University.

The ideal way to estimate “seroprevalence” — the percentage of people with antibodies to the virus — is to randomly sample households, which is time-consuming and labor-intensive. And persuading large numbers of families to have blood drawn from healthy children is likely to be a losing proposition.

I know my child had COVID. Does she still need the vaccine?

Skipping vaccination would be a gamble, experts said. There are many unanswered questions about the strength and durability of immunity in children.

“There are too many unknowns on that, whereas the vaccine is known — that’s my caution,” said Dr. Peter Chin-hong, an infectious disease expert at the University of California, San Francisco. “Certainly, I wouldn’t put all my eggs into the previous infection, natural immunity basket.”

I’m worried about side effects. Is the vaccine safe?

All of the evidence so far indicates that the vaccines are far safer than a bout of COVID-19, even for children.

For example, although the vaccines have been associated with the rare chance of myocarditis, inflammation of the heart, in young men, the symptoms have quickly resolved in most of them. COVID19 is much more likely to cause myocarditis, and a much more severe version.

“At the end of the day, acquiring immunity through infection is risky business,” Hensley said.