An online survey was conducted to compare the safety, tolerability and reactogenicity of available COVID-19 vaccines in different recipient groups. This survey was launched in February 2021 and ran for 11 days. Recipients of a first COVID-19 vaccine dose ≥7 days prior to survey completion were eligible. The incidence and severity of vaccination side effects were assessed. The survey was completed by 2002 respondents of whom 26.6% had a prior COVID-19 infection. A prior COVID-19 infection was associated with an increased risk of any side effect (risk ratio 1.08, 95% confidence intervals (1.05-1.11)), fever (2.24 (1.86-2.70)), breathlessness (2.05 (1.28-3.29)), flu-like illness (1.78 (1.51-2.10)), fatigue (1.34 (1.20-1.49)) and local reactions (1.10 (1.06-1.15)). It was also associated with an increased risk of severe side effects leading to hospital care (1.56 (1.14-2.12)). While mRNA vaccines were associated with a higher incidence of any side effect (1.06 (1.01-1.11)) compared with viral vector-based vaccines, these were generally milder (p < 0.001), mostly local reactions. Importantly, mRNA vaccine recipients reported a considerably lower incidence of systemic reactions (RR < 0.6) including anaphylaxis, swelling, flu-like illness, breathlessness and fatigue and of side effects requiring hospital care (0.42 (0.31-0.58)). Our study confirms the findings of recent randomised controlled trials (RCTs) demonstrating that COVID-19 vaccines are generally safe with limited severe side effects. For the first time, our study links prior COVID-19 illness with an increased incidence of vaccination side effects and demonstrates that mRNA vaccines cause milder, less frequent systemic side effects but more local reactions.
Keywords: COVID-19; COVID-19 vaccine; Coronavirus Disease 2019; adverse events; reactogenicity; safety; tolerability.