In November 2021, the FDA and CDC signed off on the Pfizer vaccine for 5- to 11-year-olds after a historic clinical trial with more than 4,500 participants, including 252 kids right here at Children's Hospital Colorado.
Who participated in the trial
Children’s Colorado was the largest study site in the country for Pfizer’s clinical trial investigating the safety and immune response of their COVID vaccine in kids ages 5 to 11. Before the trial began in the summer of 2021, families representing approximately 5,000 children expressed interest in joining the trial here. We then reviewed the eligibility of those who expressed interest, and ultimately enrolled 252 participants through our site.
How the study worked
Each child was randomly assigned to receive either the study vaccine (2 out of 3 participants) or a placebo (1 out of 3 participants). They received 2 injections approximately 3 weeks apart. Neither the family nor the doctors knew whether the child received the study vaccine or placebo until their follow-up visit six months after the second injection.
When the vaccine was authorized for this age group in November 2021, trial participants were “unblinded,” and participants who received the placebo were invited to receive the vaccine at Children’s Colorado.
While experts have enough data to determine that the vaccine’s benefits outweigh the risks, we’ll continue to learn more as this and other clinical trials progress. Over the course of two years, trial participants will have scheduled follow-up study visits and will track any changes in their child’s health in an electronic diary. This exact process is taking place at study sites across the world.
Results of Pfizer’s clinical trial in kids 5 to 11
Pfizer's study demonstrated that a schedule of two 10-microgram doses of the Pfizer vaccine (equivalent to one-third of the dose for older children and adults) given 21 days apart was found to be "safe, immunogenic, and efficacious" in children 5 to 11 years of age.
In other words, the two-thirds of trial participants who received the vaccine reported no serious adverse events and showed robust immune response, and the vaccine was found to be more than 90% effective at preventing COVID-19. The trial findings were presented to the FDA, CDC and published in the New England Journal of Medicine.