The Food and Drug Administration’s vaccine advisory committee had been planning to consider a two-dose regimen of the shot Tuesday. The delay is to allow the company and its partner BioNTech SE to gather and evaluate more information on the impact of a third dose, agency officials said in a statement.

“Based on the agency’s preliminary assessment, and to allow more time to evaluate additional data, we believe additional information regarding the ongoing evaluation of a third dose should be considered as part of our decision-making for potential authorization,” Acting Commissioner Janet Woodcock and Peter Marks, director of FDA’s Center for Biologics Evaluation and Research, said in the statement. 

Pfizer shares declined 0.4% at 2:09 p.m. 

Concerned about the emergence of new, highly transmissible variants like omicron, many parents are eager for their younger children to get vaccinated. However, enthusiasm for the Pfizer formulation was tempered in December when a study showed two doses failed to meet a laboratory standard for effective immune response in 2- to 4-year olds, although it did in those from six to 24 months of age. 

Data on a third dose are expected in April, the companies said. That stands to delay U.S. plans for a special vaccination program for kids under five. The government has secured sufficient supplies for all 18 million kids from six months through 4 years old, White House coronavirus response coordinator Jeff Zients said Wednesday in a press conference.

Yet there are already signs that some parents could be slow to get shots for younger children. Covid-19 vaccinations among kids ages 5 to 11 years have fallen to their lowest levels since the shots were first cleared, according to recent data from the CDC.