Background: The coronavirus disease 2019 (COVID-19) has been sabotaging the world over the last two years and vaccine is one of the key solutions. However, the concerns over its side effects can cause vaccine refusal, subsequently affecting many countries’ education system recovery plans.

Objective: To actively evaluate adverse effects and their severity following COVID-19 immunization among schoolchildren aged 12 to 17 years, to support parents’ decision-making.

Materials and Methods: The present study was an observational study whereby a Google-form survey on Pfizer COVID-19 vaccine adverse effects (CVAE) was responded between January and April 2022 by 537 participants. Descriptive statistics were used to analyze basic characteristics. Chi-square tests were performed for comparative analyses between junior (aged 12 to 15 years) versus senior (aged 16 to 17 years) high school students, and McNemar’s test for the first dose versus second dose groups analysis with a significance level set at p-value less than 0.05.

Results: At least one CVAE was reported in 93.85% of the included participants, albeit mostly mild. The most common symptom as a local event was tenderness at the puncture site (82.50%), whereas systemic events were predominated by myalgia (74.67%). The second dose was associated with increased frequency and severity of adverse effects compared to the first dose (p<0.001). The older age group had significantly more side effects compared to the younger group (p<0.05).

Conclusion: The high incidence of CVAEs in schoolchildren was predominated by mild symptoms, with the second dose and older group associated with increased frequency of symptoms. The predominance of mild symptoms found in the present study may help reduce the concerns of parents over CVAEs, ultimately accelerating vaccine coverage in the children group, which is still a gap in vaccine administration.

Keywords: Coronavirus 2019; COVID-19 Vaccine; BNT162b2; Side effects; Adverse events; Adolescence

DOI: 10.35755/jmedassocthai.2023.02.13748

Received 26 September 2022 | Revised 2 December 2022 | Accepted 14 December 2022