[Reactogenicity Study of mRNA Vaccines Against COVID-19]

To compare the reactogenicity between the types of mRNA Commirnaty® (Pfizer) and Spikevax® (Moderna) vaccines against COVID-19 in a healthcare population.

Cross sectional study of short-term adverse effects and their consequences (sick leave, limitations of daily life, etc.) after the administration of the first and second doses of both vaccines in professionals and students of a health institution. A questionnaire on symptoms and their consequences was administered seven days after each vaccination dose. The prevalence and 95% confidence interval (95%CI) were calculated. Differences between vaccines were quantified using the odds ratio (OR) and its 95%CI.

The questionnaire was completed by 1924 and 1170 healthcare providers (response rates 62.2% and 39.1%) after the first and second doses, respectively, of the Commirnaty® vaccine, and 410 (56.0%) and 107 (15.0%) of Spikevax®. After the first dose of Comirnaty®, 67.4% presented some adverse effect, and 76.1% for Spikevax® (OR 1.5 95%CI 1.2-1.9). In general, women and young people showed greater reactogenicity and differences between vaccinSpain. Consequences of adverse effects were more frequent for Spikevax®. The reactogenicity was higher after the second than the first dose, for both vaccines (Comirnaty®: 67.4% vs. 75.6%; Spikevax®: 76.1% vs. 87.9%.

The greater reactogenicity and its consequences, for the first and second dose of the Spikevax® vaccine compared to Comirnaty®, and of the second dose compared to the first dose of both vaccines, provides useful knowledge for planning vaccination against COVID-19 campaigns in healthcare settings.