(Reuters) – The U.S. Food and Drug Administration announced Friday that it had postponed a meeting of an advisory panel to consider authorization. Pfizer (NYSE:) BioNTech’s COVID-19 vaccine is available for infants 6 months to 4 years old.

The companies also stated in a separate statement that they plan to increase the time required to submit data to U.S. regulators regarding the shot for children below 5.

U.S. regulators are currently considering vaccines for this age group, even though initial results in 2 to 4 year olds were below expectations.

Pfizer announced in December that it would amend its clinical trial in order to test a three dose version of the vaccine. The low-dose version generated an inferior immune response in children aged 2-4 years. This was in contrast to what was observed in 16-25 year olds.

At the FDA’s request, the companies said that they provided data about the initial two doses for a possible three-dose regimen. The companies stated on Friday that they would have data for three-dose protection available by April 1.

Some scientists were skeptical of the idea and suggested that regulators should wait until they have data from another shot before issuing authorization.

The vaccine produced an immune response similar to that seen in 16- and 25-year olds in very young children aged between six months and two years, according to the companies.