Protective Immunity After SARS-CoV-2 Infection in Healthcare Workers — Unfinished Answers

The degree and duration of antibody-derived protection against SARS-CoV-2 reinfection is uncertain. To better understand this relation, investigators conducted a prospective longitudinal cohort study assessing incidence of PCR-positive SARS-CoV-2 infection in healthcare workers (HCW) at four Oxford University Hospitals. They measured baseline anti-spike (primary analysis) and anti-nucleocapsid IgG antibodies in >12,000 staff members who were then followed for up to 31 weeks.

At baseline, 90.6% of HCW were seronegative and 9.4% were seropositive for anti-spike IgG. During follow-up, 223 seronegative HCW tested PCR-positive for SARS-CoV-2 (1.09 per 10,000 days at risk) compared with 2 HCW who were positive for anti-spike antibody (0.13 per 10,000 days at risk). Incidence of PCR-positive symptomatic infection in seronegative HCW was 0.6 per 10,000 days at risk. Among those positive for anti-spike and anti-nucleocapsid antibodies, incidence of PCR-positive infections was inversely associated with antibody titers. In 2 of 3 HCW with possible reinfection, baseline antibody tests were discordant; the number of days between initial symptoms or seropositivity and eventual positive PCR results ranged from 160 to 199.