Moderna is expected to submit a formal request to the Food and Drug Administration on Thursday to have its Covid-19 vaccine approved for children under the age of six.

The request comes a month after the drug company announced that its two-dose regimen provided immune protection in children as young as young adults, and as lawmakers and parents wait for the administration to approve a vaccine for the country’s youngest children.

However, Moderna must still submit final datasets to the agency, which two sources familiar with the situation say will most likely not happen until May 4. Before authorizing any vaccines for young children, the FDA has also committed to holding a meeting of its outside advisory committee.

The FDA can now begin to consider whether Moderna’s shot should be made available to the general public as a result of the filing. However, a decision could take weeks.

Top FDA vaccine regulator Peter Marks told lawmakers Tuesday that the agency planned to publish a tentative timeline next week showing when it planned to hold outside advisory committee meetings on the vaccines for young children — a move that could provide more precise insight into when the agency plans to authorize the shots. Marks was questioned by Sen. Patty Murray (D-Washington).

“Just remember,” Marks told the Senate HELP Committee, “we can’t actually finish our reviews until we have complete applications in the FDA.”

“We will proceed with all due speed, once we have complete applications, some of these are complicated because they are relatively covering larger swaths of the pediatric population than others,” he added.

Moderna is also expected to seek authorization for children ages 6 to 11 and update its emergency use authorization for adolescents ages 12 to 17, according to people familiar with the situation, though it’s unclear when those applications will be officially filed. Pfizer and BioNTech currently manufacture the only Covid-19 vaccine for children aged 5 to 11.

Some federal regulators privately argued that approving the competing vaccines at the same time would make it easier for the agency to distribute them to the public and reduce the risk of confusion. Pfizer’s vaccine, unlike Moderna’s, is a three-shot regimen.

However, waiting until June would likely mean prolonging the wait for the first Covid shot for millions of children and provoking backlash from parents’ groups and lawmakers.

According to two people familiar with the situation, the criticism sparked a scramble behind the scenes to deal with the fallout, with health officials debating how to proceed once Moderna’s full filing is submitted in early May.

“Let me be very clear: being thorough does not mean we are delaying review of these vaccines,” Marks said in a video released by the FDA on Tuesday, emphasizing the importance of ensuring parents have confidence in any authorized vaccines.

According to the people, the White House has made it clear that the FDA has sole authority over the decision. Some officials have gone out of their way in the last week to avoid discussing the vaccines with FDA regulators for fear of being accused of political meddling.

Evidence from a clinical trial involving approximately 6,700 children is expected to be used in the application. Moderna announced in March that two quarter doses of its Covid-19 vaccine produced an immune response in children aged 6 and under that was comparable to that of young adults who received two full doses of the vaccine. During Omicron, real-world evidence showed that the vaccine reduced symptomatic Covid-19 cases by 43.7 percent in children aged 6 to 24 months and 35.7 percent in children aged 2 to 6 years, which was comparable to adult protection at the time.

The vaccine had only minor side effects in the children who received it, and none of the children in the study developed severe Covid-19.

Initially, the FDA told vaccine manufacturers that their products needed to reduce symptomatic Covid cases in adults by 50%. The agency issued guidance allowing manufacturers to use a metric called immunobinding, which compares the immune response generated by vaccines, for children and other groups that are more difficult to study in large numbers.