Alejandra and Marisol Gerardo are nine years old but already making a little bit of history. The twin sisters are among the first young children to get vaccinated with a COVID-19 shot in Pfizer-BioNTech’s study of its vaccine in kids under age 12.
Alejandra and Marisol had their blood drawn in the morning on March 24, then got their first dose of the two-dose vaccine later that afternoon at Duke University Medical Center, one of four study sites in the U.S. for the trial. “Their primary concern was, ‘is it going to hurt,’” says their father, Dr. Charles Gerardo, chief of emergency medicine at Duke University School of Medicine. “They’re not too worried about the long term side effects; they’re looking at the moment, not the future.”
Testing the vaccine in younger children will answer critical questions about how much immunity the shots can provide, and potentially give parents and education officials more confidence in re-opening schools. While it appears that younger children don’t get as sick with COVID-19 as older teens and adults do, how these children’s immune systems respond to the virus, and to the vaccine, remains a black box. The trial will also help provide some clarity on those questions.
Pfizer-BioNTech says it will test the same vaccine that is currently authorized for emergency use in the U.S. for those 16 years and older, but this time in children aged six months to 11 years. The company is currently wrapping up a study of its two-dose shot in adolescents aged 12 to 15 years in the U.S. and Europe.
The latest pediatric trial will follow the same three-phased approach as the adult study, with Phase 1 involving 144 children aged five to 11 years at Duke, Boston Children’s Hospital, Cincinnati Children’s Hospital and Johns Hopkins, who will all receive the vaccine but be randomly assigned one of three dosages. If the vaccine is safe in this age group, children aged two to four years will be tested, and if safe in that group, the youngest children from six months to two years will get the vaccine. Depending on the immune responses these children generate, the scientists at Pfizer-BioNTech will make a decision about the safest and most effective dose with which to proceed in its Phase 2 and Phase 3 studies.
Those will include a total of about 4,500 children broken down in the same age categories, this time randomly assigned to receive either the vaccine or placebo in a 2:1 ratio. The results will be analyzed after six months to determine if the children receiving the vaccine both generated a stronger immune response than those getting placebo, and that the response was on par with responses in vaccinated adults. If that’s the case, then Pfizer-BioNTech will submit the data to the U.S. Food and Drug Administration to expand authorization to younger children, and hopefully start vaccinating them by early next year.
Dr. Emmanuel Walter, professor of pediatrics and chief medical officer at the Duke Human Vaccine Institute who is overseeing the trial there, says the study will answer important questions about the safety and dosing of the vaccine for children—specifically whether younger children will need a different dose than adolescents and adults. The trial will test a dose about one-third that of the current adult dose, another that is about half of the adult dose, as well as the adult dose. While the Pfizer-BioNTech COVID-19 shot is the first mRNA technology-based vaccine of any kind to gain FDA authorization, Walter says it’s likely to be safe in children. “I don’t think it’s the platform so much that I would worry about for young children—I feel comfortable giving the mRNA to young children. I think the questions of will they have side effects, will the vaccine be tolerable to children, and do we need to use a smaller dose in young kids, are the biggest things.”
So far, Walter says that they have seen an “overwhelming” response to the pediatric trial, with parents like the Gerardos expressing interest in enrolling their children. Both Gerardo and his wife, who is an infectious disease physician at Duke, are vaccinated, and he says before his daughters joined the trial, they discussed volunteering with the girls. “They understand that the results are going to impact other kids, and that’s one of the lessons we wanted to teach them with this experience,” he says. “That this was one of the ways to contribute to help other people.”
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