The administration of president Joe Biden had targeted February 2022 to roll out a vaccine for those five and under;  however, at that time neither Pfizer/BioNTech nor Moderna was able to submit data on the number or strength of the juvenile doses needed.

On May 23, Pfizer and BioNTech released preliminary findings from a clinical trial with youngsters in the appropriate age group showing that three doses of their reduced-strength Comirnaty-branded shot produced a strong enough immune response to meet the criteria for emergency use authorization. Their candidate is formulated at the 3-µg dose level, a tenth of the strength offered to adults.

In the trial, the companies said the third dose was well tolerated among 1,678 children five years of age or less, with a safety profile similar to a placebo. For the three doses together, efficacy at preventing symptomatic infection was around 80.3% in the trial conducted at a time when Omicron was the predominant variant, Pfizer/BioNTech said.

Comprehensive results of the study are due to be released in June, although the partners said it could take longer to judge efficacy data as only 10 children enrolled in the trial actually became ill with Covid. This was half the number required to render the data conclusive.

BioNTech, which receives the official regulatory clearance for the vaccines based on its proprietary technology, said the vaccine makers would complete their application to the FDA for an EUA before the end of May. Comirnaty is already authorized for children aged six to 12.

Moderna is seeking clearance for its Spikevax in children aged six to 12 as well as those under six. For the younger group it is proposing a two-dose regime formulated at 25% of its 50-µg single adult dose, yielding a total dosage of 25 µg.  The Maryland-based biotech said it expects that a third dose could be needed as a booster, but has not yet submitted data on that to FDA.

In its late-April filing to the FDA for emergency clearance, Moderna said that in trials with the under-five group results showed that, when given a dose a quarter as strong, participants had a similar immune response to that of young adults.

At the time, the US vaccine maker said the results indicated that its shot could be 51% effective against symptomatic infection in children younger than two years and 37% effective among those aged two to five.

Experts said it was unclear why the Moderna shot would be less effective than its competitor’s despite the latter’s higher dosage. The meeting of the FDA’s advisory panel to discuss and compare the pediatric vaccine candidates has been postponed from May to mid-June in anticipation of the receipt of Pfizer/BioNTech’s updated application.

Pfizer/BioNTech’s Phase 1/2/3 trial enrolled more than 10,000 children aged six months to under 12 years of age in the US, Finland, Poland and Spain at more than 90 clinical trial sites. The trial evaluated the safety, tolerability and immunogenicity of three doses of Comirnaty in three age groups: five years to under 12 years; two years to under five years and six months to under two years.

Author: Dede Williams, Freelance Journalist