SARS-CoV-2-Specific Neutralizing Antibody Responses in Norwegian Health Care Workers after the First Wave of COVID-19 Pandemic: A Prospective Cohort Study

Background: During the coronavirus disease 2019 (COVID-19) pandemic, many countries experienced infection in health care workers (HCW) due to overburdened health care systems. Whether infected HCW acquire protective immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is unclear. Methods: In a Norwegian prospective cohort study, we enrolled 607 HCW before and after the first COVID-19 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/IgA antibodies increased after the first wave in HCW with, but not in HCW without, COVID-19 patient exposure. Thirty-two HCW (5.3%) had spike-specific antibodies (11 seroconverted with ≥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, 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.