The Phase 2/3 trial included 1,678 children who received a third dose during the period when the Omicron coronavirus variant dominated. Antibody levels tested one month after the third dose showed the vaccine produced a similar immune response as two doses in 16-to-25 year-olds, the companies said in a news release. The data has not yet been peer-reviewed or published.
Midtrial results found vaccine efficacy of 80.3% against symptomatic Covid-19 in this youngest age group. The companies identified 10 symptomatic cases at least seven days after the third dose. However, the efficacy rate won’t be finalized until at least 21 symptomatic cases are found in the vaccine group and then compared with the number of symptomatic cases in the placebo group.
The companies said three child-size doses for this youngest age group were “well-tolerated” and no new safety signals were identified.
“These topline safety, immunogenicity and efficacy data are encouraging, and we look forward to soon completing our submissions to regulators globally with the hope of making this vaccine available to younger children as quickly as possible, subject to regulatory authorization,” Pfizer Chairman and CEO Albert Bourla said in a statement.
The vaccines for this youngest age group are smaller than those used in older age groups. People age 12 and older receive two doses of a 30-microgram vaccine and children ages 5 to 12 receive two doses of a 10-microgram vaccine. Both age groups are eligible for booster doses.
For children 6 months to 5 years, the Pfizer/BioNTech vaccine is three 3-microgram doses. The initial two doses were given three weeks apart, and the third dose was given at least two months after their second dose.
Children younger than 5 are the only age group not yet eligible for vaccination against Covid-19. The vaccine for this age group was delayed when results of a two-dose series of the Pfizer/BioNTech vaccine didn’t provide the expected level of protection. The companies said they would amend the trial to add a third dose.
In February, the US Food and Drug Administration asked the companies to submit a request for emergency use authorization based on the two-dose data, but then postponed a meeting of the agency’s vaccine advisory board so the third-dose data could be considered.
The FDA’s Vaccines and Related Biological Products Advisory Committee has tentative meetings scheduled for June 8, 21 and 22 to discuss emergency use authorizations updates that could make younger children eligible for vaccination with the Moderna or Pfizer/BioNTech vaccines.
Moderna submitted its vaccine data for children 6 months through 5 years of age to the FDA in late April. Moderna’s submission is based on two 25-microgram doses given 28 days apart.