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For a video interview with Shane Crotty, PhD, click here.

If he had a kid who was 5 to 11 years old, Shane Crotty, PhD, a virologist at the La Jolla Institute for Immunology in California, would get them the Pfizer vaccine right away.

That's largely because of the dose, Crotty said.

"Even if the Moderna vax were available, I would go with the Pfizer vax for my kids. Because the Pfizer vaccine is a 10 mcg dose," .

That's just a third of the adult dose of the Pfizer vaccine (30 mcg), yet it boosted neutralizing antibodies to similar levels as 20-year-olds given the adult dose, he said.

"Given that kids generally have a much milder course of COVID-19 disease, having a level of immunity equal to that of young adults ... should be more than enough for a 5-11 year old," .

At the same time, the data showed that the 10-mcg dose had "pretty low side effects" in this age group, he noted.

One of parents' main concerns has been myocarditis, especially in young boys. While Crotty acknowledged that the mRNA vaccines carry a very low risk of the condition overall, he highlighted a large difference in dose in the younger age group between the Pfizer and Moderna shots.

Moderna is currently -- just half of its adult dose -- in kids ages 6 to 11.

"The myocarditis risk from the mRNA vaccines is small, but it is real, and I operate on the assumption that the 50 mcg Moderna has somewhat higher risk than 10 mcg Pfizer. That may not be true," with appropriate caution.

The Moderna vaccine still isn't approved for kids ages 12 to 17, even though the company announced topline data from that trial and applied for FDA emergency use authorization (EUA) for the indication .

Over the weekend, that the FDA said it needs more time to evaluate the company's shot in kids ages 12 to 17 (which was submitted as a 100-mcg 2-dose series). The company said FDA is looking specifically at the risk of myocarditis in this population -- adding that the agency's review may not be completed before January 2022.

Moderna also said it would delay filing for an EUA for the smaller, 50-mcg dose of its vaccine in 6-to-11-year-olds while FDA completes its review.

Experts at both the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) meeting and CDC's Advisory Committee on Immunization Practices (ACIP) meeting on Pfizer's vaccine for 5-to-11-year-olds pointed out the odd cutoff for dosing in kids who are 11 versus 12 years old.

Arnold Monto, MD, chair of the VRBPAC meeting, asked if the lower 10-mcg dose could be used in kids ages 12 to 15.

William Gruber, MD, of Pfizer's vaccine clinical research and development team, responded that there's "potential for the 10-mcg dose to provide antibody response" in this age group and that there's also potential to look at that in the future -- "particularly as we move out of the pandemic period."

Monto replied that the lower dose would be expected to diminish potential side effects like myocarditis: "We may want to look at that dose in" 12-to-15-year-olds, he said.

At the ACIP meeting, Doran Fink, MD, PhD, a deputy director at FDA's Center for Biologics Evaluation and Research, said FDA supports a "flexible" choice for this age group, where an 11-year-old who got 10 mcg for their first dose can get a 30-mcg second dose if they turn 12 in the interim -- but noted CDC needs to make the final decision.

ACIP officials stated that the dose should be based on the child's age on the day of vaccination. But if a child turns 12 between the first and second dose, and gets 10 mcg for the second dose, they don't need to repeat the dose, as that's "not considered an error per the EUA," the slide stated.

Still, Crotty emphasizing the overall safety of vaccinating kids: "I certainly think choosing Moderna is fine!" he noted. "But, of course, most parents won't have that option for a while. And the risk:benefit ratio tilts more towards Pfizer for me for kids. Whereas, in adults I think it tilts towards Moderna."

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