Background Children 6 months to < 5 years old are recommended to receive 3-dose regimen of BNT162b2. Children previously infected with Omicron variant of SARS-CoV-2 develop immunity from natural infection, therefore may require fewer doses of vaccine. Objective To compare immunogenicity of 1- or 2-dose BNT162b2 in healthy children post COVID-19 with 3-dose BNT162b2 in COVID-naïve children. Methods Children aged 6 months to < 5 years who developed COVID-19 during the Omicron-predominant period were enrolled; Group A 3–6 months(N = 40) and Group B > 6 months(N = 40) prior to vaccination. Participants in Group A and B received 2-dose BNT162b2 intramuscularly 1 month apart. COVID-naïve children were enrolled as a control group (N = 40) and received 3-dose BNT162b2 at month 0,1,3. Neutralizing antibody against Omicron variant(BA.2.75 and BA.4/5) was determined by pseudovirus assays(pVNT) as reported by neutralization dilution for 50%inhibition (ID 50}) at 28 days after the 1^{st} and 2^{nd} dose. Results From October-November 2022, 120 children with a median age of 2.8 years (IQR 1.6–4.0) were enrolled. The median duration since COVID-19 to vaccination was 4.4 months(IQR 3.8–5.4) in Group A and 7.9 months(7.0–8.5) in Group B. In Group A, the geometric means(GMs) of pVNT-BA.2.75 ID 50} were 553 (95%CI 338–906) and 753(516–1098) after 1 and 2 doses, respectively, and the GMs of pVNT-BA.4/5 ID 50} were 1936(1402–2673) and 1885(1414–2512), respectively. In Group B, the GMs of pVNT-BA.2.75 ID 50} were 1383(1100–1742) and 1419 (1104–1823), and the GMs of pVNT-BA.4/5 ID 50} were 2627(2048–3367) and 2056(1546–2735), respectively. Meanwhile in COVID-naïve group, the GMs of pVNT-BA.2.75 and pVNT-BA.4/5 ID 50} were 158(98–255) and 59(31–114) after the 3^{rd} dose, respectively. The geometric mean ratio(GMR) of pVNT-BA.2.75 ID 50} after 1 dose in Group A and B compared with after 3 doses in COVID-naïve group were 3.50 (1.93–6.34) and 8.74 (4.79–15.95), respectively. The GMR of pVNT-BA.2.75 ID 50} after 1 dose in Group B compared with Group A was 2.50 (1.45–4.31). Conclusions Children previously infected with SARS-CoV-2 Omicron variant, developed robust neutralizing antibody response against Omicron variant after single-dose BNT162b2. Children with an interval of > 6 months since COVID-19 infection developed higher neutralizing antibody response compared to those with a 3-to-6-month interval.
【저자키워드】 BNT162b2 vaccine, SARS-CoV-2 vaccine, Infant, anti-SARS-CoV-2 IgG, Child, Neutralizing antibody titer,