Abstract
Objective: To compare the reactogenicity and immunogenicity between the two-dose mRNA COVID-19 vaccine regimen and one or two doses of inactivated vaccine followed by an mRNA vaccine regimen in healthy children between 5-11 years of age. Methods: A prospective cohort study was performed at King Chulalongkorn Memorial Hospital in Thailand between March to June 2022. Healthy children between 5-11 years of age were enrolled and received the two-dose mRNA COVID-19 vaccine (BNT162b2) regimen or the inactivated (CoronaVac) vaccine followed by the BNT162b2 vaccine regimen. In addition, healthy children who received two doses of BBIBP-CorV between 1-3 months prior were enrolled to receive a heterologous BNT162b2 as a third dose (booster). Reactogenicity was assessed by a self-reported online questionnaire. Immunogenicity analysis was performed to determine binding antibodies to wild-type SARS-CoV-2. Neutralizing antibodies to Omicron variants (BA.2 and BA.5) were tested using the focus reduction neutralization test. Results: Overall, 166 eligible children were enrolled. Local and systemic adverse events which occurred within 7 days after vaccination were mild to moderate and well-tolerated. At one-month, post-two or post-three doses, children vaccinated with two-dose BNT162b2 (GMT 2872 BAU/mL), CoronaVac/BNT162b2 (GMT 3021 BAU/mL), and two-dose BBIBP-CorV followed by BNT162b2 (GMT 3269 BAU/mL) elicited similar levels of anti-receptor-binding domain (RBD) IgG (ns). However, the two-dose BNT162b2 and two-dose BBIBP-CorV followed by BNT162b2 groups elicited higher neutralizing activities against Omicron BA.2 and BA.5 variant than the CoronaVac/BNT162b2 group. Conclusion: The heterologous, CoronaVac vaccine followed by the BNT162b2 vaccine, regimen elicited lower neutralizing activities against the emerging Omicron BA.2 and BA.5 variant than the two-dose mRNA regimen. A third dose (booster) mRNA vaccine should be prioritized for this group.
