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The FDA has for children as young as 6 months of age, the agency announced on Friday.

The emergency use authorization (EUA) for Pfizer-BioNTech's vaccine -- which is already authorized or approved in individuals 5 years and older -- will now include children ages 6 months to 4 years. Moderna's EUA will now include children and adolescents ages 6 months to 17 years (the vaccine is approved for use in adults).

"Many parents, caregivers, and clinicians have been waiting for a vaccine for younger children and this action will help protect those down to 6 months of age," FDA Commissioner Robert Califf, MD, said in a statement. "As we have seen with older age groups, we expect that the vaccines for younger children will provide protection from the most severe outcomes of COVID-19."

"While COVID-19 does affect older and immunocompromised populations more adversely than young children, young children can still suffer the severe consequences of COVID-19, including severe illness and death," Califf warned during a press briefing following the announcement.

The move follows 2 days of deliberation by the agency's Vaccines and Related Biological Products Advisory Committee (VRBPAC), which unanimously endorsed both mRNA vaccines in the youngest age group, as well as the older group of children and teens in the case of Moderna's vaccine.

Asked by reporters how parents of young children should decide between the two vaccines, Peter Marks, MD, PhD, director of the agency's Center for Biologics Evaluation and Research, said "the correct answer here is whatever vaccine your healthcare provider, pediatrician has. That's what I would give my child."

"It may be that the Moderna vaccine brings an immune response slightly more rapidly," said Marks. "On the other hand, the three-dose Pfizer regimen may also bring a greater immune response after the third dose. And there are some subtle differences in the safety profile."

On the possibility of potential strain changes, Marks noted that these available vaccines offer "excellent foundational immunity" against a broad range of COVID variants already. "I would have children start this right now."

Marks said he does not anticipate substantial delays if younger children should need a vaccine with an updated strain down the line. "I say 'if' because we will have to see where the data take us."

Pfizer's Vaccine

Data supporting the effectiveness in children 6 months to 4 years were based on immunobridging criteria and showed that three doses (3 mcg each, second dose given after 3 weeks and the third at least 8 weeks later) resulted in similar immune responses compared with teens and adults ages 16-25 years who received a primary series at the recommended dosage for their age group. Typical efficacy data were "determined not to be reliable due to the low number of COVID-19 cases that occurred in study participants," the FDA noted.

Safety analyses involved approximately 400 children who received the vaccine in the 6- to 23-month age group and 600 in the 2- to 4-year age group, with 2 months of safety data following the third dose. Commonly reported adverse events (AEs) in the younger group included irritability, decreased appetite, fever, and pain, as well as injection-site tenderness, redness, or swelling. In the older group, vaccine AEs included these plus headache and chills.

Moderna's Vaccine

Immunobridging criteria were also used as the primary support for Moderna's vaccine in children ages 6-23 months and 2-5 years. With a two-dose 25-mcg primary series, the two groups achieved similar immune responses when compared with an adult group receiving the adult mRNA doses. Efficacy data involving 5,400 children showed a vaccine efficacy of 50.6% following the second dose in the younger group and 36.8% for the older children during a period when Omicron was circulating.

Similarly, children ages 6-11 years (two 50-mcg doses) and adolescents ages 12-17 years (two 100-mcg doses) had similar immune responses to an adult comparator group. Efficacy analyses were again not "reliable" in the younger group, but vaccine recipients in the 12-17 group had a 93.3% vaccine efficacy during a pre-Omicron study period.

For the younger subset, safety data involved 1,100 vaccine recipients ages 6-23 months and 2,200 recipients ages 2-5 years, with 2 months of follow-up data. Commonly reported AEs across all ages included pain, injection-site redness or swelling, fever, and lymph node swelling or tenderness in the underarm or groin. In the younger group, irritability or crying, sleepiness, and loss of appetite were also observed. In the 2- to 5-year age group, AEs also included fatigue, headache, muscle ache, chills, nausea or vomiting, and joint stiffness.

For the older group, safety analyses were derived from 3,000 children ages 6-11 years and 2,500 adolescents ages 12-17 years, most of whom had 2 months of safety data. Common AEs included pain, redness, and swelling at the injection site, as well as fatigue, headache, muscle or joint pain, chills, swollen lymph nodes in the injection-site arm, nausea or vomiting, and fever.

No cases of myocarditis or pericarditis occurred in either company's trial, but the FDA noted that a higher risk has been observed with the mRNA vaccines in males ages 12-24 years. Both Moderna and Pfizer will monitor for cases of these AEs as part of the terms of their EUAs.

Washington Correspondent Shannon Firth contributed to this report.

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