Why the trial data supports covid-19 vaccines for children

On Tuesday, a panel of experts at the FDA will meet to discuss whether Pfizer’s covid vaccine should be approved for 5-to-11-year-olds in the US. If that group says yes, the decision will go to the CDC’s immunization advisory board, known as ACIP, which meets next week. According to Anthony Fauci, if both those groups give the thumbs up, vaccinations for millions of children could begin in early November—with the potential for most children to be fully vaccinated by the holidays.

But not every country is following the same path as the US: some are trying single doses, or holding back vaccines from younger children.

So if youngsters are at far lower risk of covid, is it really necessary to vaccinate them? What are the benefits individually? And what about for society more generally?

“The most important thing is that when we’re giving a vaccine to generally healthy people and generally healthy children, the bar is set very high,” says Dean Blumberg, an associate professor of pediatric infection diseases at UC Davis. “There clearly needs to be a benefit to the individual child.”

That’s why, when officials meet, they will weigh up a complicated set of factors. What are the chances that a child will be infected with covid? How much protection does a vaccine provide? What are the potential symptoms and complications children face from taking it? 

Taking all these questions into account, says Blumberg, “it’s clear the benefits outweigh the risks for this age group.”

In fact, the trial data and analyses showed that in almost every covid scenario, vaccinating children will prevent severe infection and death, with very little risk.

What the studies found

Pfizer’s study, which started in March 2021, took nearly 2,300 children and gave two-thirds of them a two-dose vaccination regimen, while the others got a placebo. Shots were given 21 days apart and, crucially, at a lower dosage than those for older people—a third of the amount of vaccine.

From the study, three vaccinated children caught covid, while there were 16 cases among the placebo group—almost 91% effectiveness. Side effects were typical and generally mild, and myocarditis, the heart inflammation that has been seen as a rare side effect and has probably caused most concern, didn’t even appear (rates among adults run at around seven per million, so 2,300 is a very small sample size).

Moderna, meanwhile, said on Monday that its studies on children under 12—with two shots at half the adult dosage given 28 days apart—also show strong results. That vaccine will not be up for discussion when the FDA meets, and will have to go through the same approval pathway that Pfizer is currently on before it can be given to children.

The bottom line is that these studies have shown that vaccinations reduce children’s chances of symptomatic covid infection and hospitalization in line with adult numbers—and without notable complications.

Could vaccinating children help curb the pandemic?

Vaccination is not just about individual benefits, however, although those are obviously important. On a broader level, says computational epidemiologist Maimuna Majumder, vaccinating children could have an impact on the shape of the pandemic itself.

“One thing that makes school age children––especially younger kids––unique is not only the number of contacts they have on a given day but also the heterogeneity of age groups among those contacts,” says Majumder, who is a faculty member at Boston Children’s Hospital and Harvard Medical School. “They interact with their peers at school and at extracurriculars, but they also interact with older educators and care-providers, as well as their families.”

Because of this, she says “we expect that widespread vaccination of younger school age children would help curb transmission in the months ahead.”

And remember: vaccinations don’t just stop most hospitalizations from covid—they also slow down the spread of the disease. Studies in Israel and the US suggest that vaccination reduces viral load, which in turn reduces transmission.

That’s important because children and adolescents have accounted for 13% of documented covid cases. The 5-11 age group is the largest remaining cohort of unvaccinated people in the US: some 28 million children around the country. That’s 8% of the population, and if they were all vaccinated, it could boost the US’s overall vaccination rate from 58% to 66%—much closer to the thresholds for herd immunity.

But that may be too high for some places to achieve. 

Ka-Kit Tung, a mathematics professor at the University of Washington, has been studying the effect of vaccines on variant spread. He says that the infectiousness of the delta variant means it’s vital to get as close to 100% vaccination as possible. 

Herd immunity from the original strain of covid needed something like 75% vaccination, but delta requires more like 99% coverage. “That is, you need to vaccinate every child and adult,” he says. “If you exclude a group of the population, you will never bring down the reproduction number to below 1.”

Getting parents on board

Is such a number realistic? Majumder notes that vaccination rates among adolescents are still low, however—just 46% of 12-15 year olds have been vaccinated so far. That, she says, is largely because of the concerns of parents.

“Because of this, I’m of the opinion that we need to re-center the conversation around parental vaccine hesitancy,” she says. “This isn’t a new problem by any means; before the pandemic, I was studying this phenomenon within the context of measles and HPV.”

Still, while children are less likely to get symptomatic covid (and therefore less likely to spread it through coughing and sneezing), vaccinating this group could make all the difference as we head into another potentially tough covid winter.

“You could think of this like influenza, and how we live with that disease,” says UC Davis’s Blumberg. Flu shots are far less effective than covid vaccines, but they still help protect people if enough people take them regularly. 

“With influenza, most people have partial immunity,” he says. “They might catch it and get better, but it doesn’t result in hospitalization or serious disease in the vast majority of people unless they’re immunocompromised or elderly.”

And if we achieve that kind of outcome, he says, “then we don’t have hospitals and ICUs being overwhelmed … and if we don’t have that, we can end lockdowns and mask mandates.”

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