The approval of Pfizer’s COVID-19 vaccine for children under five in the United States has hit a snag.

On Friday, Pfizer announced it’s postponing its application with the Food and Drug Administration to approve its COVID-19 for children between the ages of 6 months and 4 years, NBC News reports. 

Pfizer requested the FDA approve its COVID-19 for young children earlier this month. But the company said Friday it will wait for data from a study evaluating administering a third dose in this age group two months after the second dose. 

“Given that the study is advancing at a rapid pace, the companies will wait for the three-dose data as Pfizer and BioNTech continue to believe it may provide a higher level of protection in this age group,” Pfizer and BioNTech said. “This is also supported by recent observations of three dose booster data in several other age groups that seems to meaningfully augment neutralizing antibody levels and real world vaccine protection for omicron compared to the two-dose regimen.”

It’s a delay in the timeline after it was previously reported that the vaccine could potentially be available for young kids by February. 

At the same time, in what The New York Times described as a “striking reversal,” the FDA announced Friday it has postponed a meeting of its Vaccines and Related Biological Products Advisory Committee to consider the Pfizer vaccine, originally scheduled for Feb. 15, as “we believe additional information regarding the ongoing evaluation of a third dose should be considered as part of our decision-making for potential authorization.” The FDA said it will provide an update on the timing of the meeting when it receives the additional data from Pfizer, which Pfizer said is expected in early April.