ABSTRACT
BACKGROUND: The purpose of this study was to assess whether influenza vaccination has an impact on the risk of coronavirus disease 2019 (COVID-19). METHODS: A cohort of 46â 112 healthcare workers were tested for antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and filled in a survey on COVID-19 symptoms, hospitalization, and influenza vaccination. RESULTS: The risk ratio of hospitalization due to SARS-CoV-2 for influenza vaccinated compared with unvaccinated participants was 1.00 for the seasonal vaccination in 2019/2020 (confidence interval, .56-1.78, Pâ =â 1.00). Likewise, no clinical effect of influenza vaccination on development of antibodies against SARS-CoV-2 was found. CONCLUSIONS: The present findings indicate that influenza vaccination does not affect the risk of SARS-CoV-2 infection or COVID-19.
Subject(s)
COVID-19 , Influenza, Human , COVID-19/prevention & control , Health Personnel , Humans , Influenza, Human/epidemiology , Influenza, Human/prevention & control , Prospective Studies , SARS-CoV-2 , VaccinationABSTRACT
OBJECTIVES: Antibodies to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are a key factor in protecting against coronavirus disease 2019 (COVID-19). We examined longitudinal changes in seroprevalence in healthcare workers (HCWs) in Copenhagen and the protective effect of antibodies against SARS-CoV-2. METHODS: In this prospective study, screening for antibodies against SARS-CoV-2 (ELISA) was offered to HCWs three times over 6 months. HCW characteristics were obtained by questionnaires. The study was registered at ClinicalTrials.gov, NCT04346186. RESULTS: From April to October 2020 we screened 44 698 HCWs, of whom 2811 were seropositive at least once. The seroprevalence increased from 4.0% (1501/37 452) to 7.4% (2022/27 457) during the period (p < 0.001) and was significantly higher than in non-HCWs. Frontline HCWs had a significantly increased risk of seropositivity compared to non-frontline HCWs, with risk ratios (RRs) at the three rounds of 1.49 (95%CI 1.34-1.65, p < 0.001), 1.52 (1.39-1.68, p < 0.001) and 1.50 (1.38-1.64, p < 0.001). The seroprevalence was 1.42- to 2.25-fold higher (p < 0.001) in HCWs from dedicated COVID-19 wards than in other frontline HCWs. Seropositive HCWs had an RR of 0.35 (0.15-0.85, p 0.012) of reinfection during the following 6 months, and 2115 out of 2248 (95%) of those who were seropositive during rounds one or two remained seropositive after 4-6 months. The 133 of 2248 participants (5.0%) who seroreverted were slightly older and reported fewer symptoms than other seropositive participants. CONCLUSIONS: HCWs remained at increased risk of infection with SARS-CoV-2 during the 6-month period. Seropositivity against SARS-CoV-2 persisted for at least 6 months in the vast majority of HCWs and was associated with a significantly lower risk of reinfection.
