Companies say that a three-dose vaccine for children aged six months to five years old is 80% effective at preventing illness.

According to recent clinical trial results from Pfizer and BioNTech, a third COVID-19 vaccine dose was well tolerated by children aged five and below, and most side effects were mild-to-moderate.

The companies say that their three-dose vaccine for children aged six months to five years old was 80% effective at preventing illness during the surge of the Omicron variant.

Pfizer and BioNTech plan to complete their application for the US Food and Drug Administration (FDA) to authorise the vaccine this week, according to BioNTech CEO, Ugur Sahin.

The clinical trial data includes 1,678 children under five who received the third shot at least two months after their second dose while Omicron was the main variant. During the Omicron surge, kids aged five years or younger were hospitalised with COVID-19 at five times the rate of the pandemic peak, according to the Centers for Disease Control and Prevention (CDC).

Kids under the age of five receive 3-microgram shots, which is one-tenth the dosage of adults. They are the only age cohort in the US that remains ineligible for vaccination.

Pfizer had initially planned to seek fast-track authorisation from the FDA earlier this year, while clinical trial results were still pending. This was delayed, however, in order to wait on data from the third dose after the first two shots were only 30% to 40% effective.

An FDA committee of independent vaccine experts is expected to meet in June regarding Pfizer’s application, as well as one from fellow vaccine manufacturer Moderna to authorise its two-dose vaccine for children under age six. Current dates have been set for 8, 21 and 22 June, according to media reports.