Safety of Pfizer-BioNTech vaccine in a cohort of healthcare providers:
differences between naïve and previously infected.
Abstract
Introduction: The Spanish Society of Immunology recently warned that a
history of past COVID-19 could result in a higher incidence of adverse
events (AEs) related to vaccination. We set out to analyze whether there
were any differences in AEs between healthcare workers vaccinated for
COVID-19 (either after the first or second dose) who had had a prior
diagnosis SARS-CoV-2 infection compared to those who had not had
COVID-19 before vaccination. Methods: This was a retrospective cohort
study in a population of healthcare workers. AEs related to the first
and second doses of the Pfizer vaccine were recorded. We compared the
incidence of AEs and compared individuals with 0–3 different AEs to
those with 4 or more AEs. The relative risks (RR) and their 95%
confidence intervals were calculated. Results: Past infection was
associated with having more AEs after the first dose (p <
0.001), but not the second one (p = 0.476), as well as a higher
incidence of AEs (p < 0.001). Common AEs that were
statistically associated with past COVID infection included arthralgia,
asthenia, fever, chills, headache, and myalgia (p ≤ 0.001). The RR for
having an increased absolute number of different AEs was 1.18 (95%CI
[1.05, 1.33]) after the first dose and 1.05 (95%CI [0.96,
1.14]) after the second dose. Conclusions: Our results showed that the
incidence of AEs was higher in individuals with a history of prior
COVID-19 infection.