CLINICAL STUDIES — Expansion of the EUAs of both vaccines was based primarily on immunogenicity data; data on the efficacy of the vaccines in preventing infection and severe disease in younger populations were generally limited by short follow-up times and low infection and hospitalization rates.

A study compared the immunogenicity of three 3-mcg doses of the Pfizer vaccine in 82 children 6-23 months old and 143 children 2-4 years old with that of two 30-mcg doses in 170 persons 16-25 years old. Geometric mean titer levels of anti-SARS-CoV-2 neutralizing antibodies 1 month after the final dose were higher in children 6-23 months old (1406.5) and 2-4 years old (1535.2) than in persons 16-25 years old (1180.0). All children 6 months to 4 years old experienced a seroresponse.2,3

Studies compared the immunogenicity of two doses of the Moderna vaccine in 230 children 6-23 months old (25 mcg), 264 children 2-5 years old (25 mcg), 320 children 6-11 years old (50 mcg), and 340 adolescents 12-17 years old (100 mcg) with that of two 100-mcg doses of the vaccine in cohorts of ~300 adults 18-25 years old. Geometric mean titer levels of anti-SARS-CoV-2 neutralizing antibodies 28 days after the second dose were at least as high in each pediatric cohort as they were in the comparator adult cohorts (1780.7 in children 6-23 months old, 1410.0 in children 2-5 years old, 1610.2 in children 6-11 years old, and 1401.7 in adolescents 12-17 years old vs 1299.9-1390.8 in adults 18-25 years old), and 99-100% of pediatric vaccine recipients experienced a seroresponse.4-6

ADVERSE EFFECTS — In a randomized, observer-blind trial, the most common adverse effects of the Pfizer vaccine in children 6-23 months old were irritability, decreased appetite, fever, and injection-site tenderness, redness, and swelling. Adverse effects in children 2-4 years old included fatigue, fever, headache, chills, muscle pain, and injection-site pain, redness, and swelling. Lymphadenopathy occurred rarely (<0.5%) in both age cohorts. Most adverse effects were mild to moderate in severity. Myocarditis and anaphylaxis due to the vaccine were not reported.2,3

In randomized, observer-blind trials, the most common adverse effects of the Moderna vaccine in children 6-36 months old were irritability, sleepiness, loss of appetite, fever, axillary or groin swelling or tenderness, and injection-site pain, erythema, and swelling. Adverse effects in older children included fatigue, headache, myalgia, arthralgia, fever, chills, nausea/vomiting, axillary or groin swelling or tenderness, and injection-site pain, erythema, and swelling. Most adverse effects were mild to moderate in severity and occurred at a higher frequency after the second dose. Myocarditis and anaphylaxis due to the vaccine were not reported.4-10

DOSAGE AND ADMINISTRATION — Children receiving the Pfizer vaccine should be given three 3-mcg primary-series doses intramuscularly; the second dose should be given 3 weeks after the first, and the third dose ≥8 weeks after the second. Alternative dosing schedules are authorized for children who will turn 5 years old during their primary series (see Table 1, footnote 4). Booster doses of the Pfizer vaccine are not currently authorized for use in children <5 years old.2

Children receiving the Moderna vaccine should be given two age-appropriate primary-series doses (25 mcg for ages 6 months-5 years, 50 mcg for ages 6-11 years, and 100 mcg for ages 12-17 years) intramuscularly 1 month apart. A third primary-series dose, equal in strength to the first two, should be administered at least 1 month after the second dose to children who have undergone solid organ transplantation or have a condition that compromises the immune system to a similar extent.11 Booster doses of the Moderna vaccine are not currently authorized for use in children <18 years old.4-6