BACKGROUND: During the coronavirus disease 2019 (COVID-19) pandemic, many countries experienced infection in healthcare workers (HCW) due to overburdened healthcare systems. However, whether infected HCW acquire protective immunity against SARS-CoV-2 is unclear. Here, we characterized SARS-CoV-2-specific antibody responses in Norwegian HCW in a prospective cohort study. METHODS: We enrolled 607 HCW pre- and post-the first COVID-19-pandemic wave. Exposure history, COVID-19-like symptoms and serum samples were collected. SARS-CoV-2-specific antibodies were characterized by spike-protein IgG/IgM/IgA enzyme-linked immunosorbent and live-virus neutralization assays. RESULTS: Spike-specific IgG, IgM, and IgA antibodies increased after the first pandemic wave in HCW with COVID-19-patient exposure, but not in HCW without patient exposure. Thirty-two HCW (5.3%) had spike-specific antibodies (11 seroconverted with &#8805;4-fold increase, 21 were seropositive at baseline). Neutralizing antibodies were found in 11 HCW that seroconverted, of whom 4 (36.4%) were asymptomatic. Ninety-seven HCW were tested by reverse-transcriptase-polymerase chain reaction (RT-PCR) during follow-up, 8 were positive (7 seroconverted and 1 had undetectable antibodies). CONCLUSIONS: We found increases in SARS-CoV-2-neutralizing antibodies in infected HCW, especially after COVID-19-patient exposure. Our data show a low number of SARS-CoV-2-seropositive HCW in a low prevalence setting, however, the proportion of seropositivity was higher than RT-PCR positivity, highlighting the importance of antibody testing.
SARS-CoV-2-specific neutralizing antibody responses in Norwegian healthcare workers after the first wave of COVID-19 pandemic: a prospective cohort study