Hybrid Immunity for COVID-19 in Bolivian Healthcare Workers

Introduction Vaccination is one of the pillars for the prevention of COVID- 19 in healthcare workers (HCWs). The present study aims to determine the effectiveness of vaccination for COVID-19 as well as hybrid immunity in previously infected HCWs in a hospital in a developing country. Methods An observational study was carried out on health personnel with a complete COVID-19 vaccination schedule according to their previous infection status, with a follow-up period of 15 months. Results In this study, 335 subjects were enrolled, of which 32.8% had a previous infection with COVID-19. The safety of vaccines was determined by estimating the presence of adverse effects of vaccination and immunization (AEVI), with the first and second doses showing an incidence of 8.2% and 9.5% respectively, during the second and third waves. Around 5.7% of immunized personnel were sick and 8.4% in the fourth wave; the serum value of neutralizing antibodies was normal at 60.2% with no differences between vaccines (p=0.164). However, in personnel with hybrid immunity, there were normal levels of antibodies in 81.8% of cases (p= 0.023), fewer days of medical leave (6.4 days (standard deviation=1.4) (p=0.067)), higher immunoglobin values (p=0.011) and an insignificantly (p=0.248) lower rate of COVID-19 presentation. Conclusion Vaccination, when applied to people who previously acquired natural immunity, generates a hybrid immunity that is robust, and could have a longer duration, as well as greater efficacy for new COVID-19 variants of concern.