Analysis of Adverse Effects of COVID-19 Vaccines in Spain following Booster Dose.

The present study evaluates the adverse effects of three vaccines: AstraZeneca (Vaxzevria), Pfizer/BioNTech (Comirnaty) and Moderna (Spikevax) according to the dose. From 733 participants collected, the vaccine schedule was as follows: 330 (45%) received a double dose of the AstraZeneca vaccine, 382 (52.1%) received a double dose of Pfizer, 18 (2.5%) received a heterologous prime boost and 3 (0.4%) received a single dose. Pfizer and Moderna vaccines were administered as a third dose in 70 and 121 individuals, respectively. Local and systemic reactions observed in the three vaccines were mild to moderate in severity. Only one AstraZeneca recipient (0.3%) presented a serious adverse effect: blurred vision. Adverse events were more frequent after the first dose of AstraZeneca and after the second dose of Pfizer. As the third dose, Moderna causes more adverse effects than Pfizer regardless of the type of vaccine previously administered, whereas the reactogenicity of a third dose of Pfizer is slightly higher in the group previously vaccinated with Pfizer than in that group with AstraZeneca. In short, secondary effects of the third dose of COVID-19 vaccines were similar to those after dose 2, but their frequency depends on the type of vaccine and the combinations of vaccines.