Prevalence and duration of detectable SARS-CoV-2 nucleocapsid antibody in staff and residents of long-term care facilities over the first year of the pandemic (VIVALDI study): prospective cohort study

Background Long Term Care Facilities (LTCF) have reported high SARS-CoV-2 infection rates and related mortality, but the proportion infected amongst survivors and duration of the antibody response to natural infection is unknown. We determined the prevalence and stability of nucleocapsid antibodies - the standard assay for detection of prior infection - in staff and residents from 201 LTCFs. Methods Prospective cohort study of residents aged >65 years and staff of LTCFs in England (11 June 2020-7 May 2021). Serial blood samples were tested for IgG antibodies against SARS-CoV-2 nucleocapsid protein. Prevalence and cumulative incidence of antibody-positivity were weighted to the LTCF population. Cumulative incidence of sero-reversion was estimated from Kaplan-Meier curves. Results 9488 samples were included, 8636 (91%) of which could be individually-linked to 1434 residents or 3288 staff members. The cumulative incidence of nucleocapsid seropositivity was 35% (95% CI: 30-40%) in residents and 26% (95% CI: 23-30%) in staff over 11 months. The incidence rate of loss of antibodies (sero-reversion) was 2.1 per 1000 person-days at risk, and median time to reversion was around 8 months. Interpretation At least one-quarter of staff and one-third of surviving residents were infected during the first two pandemic waves. Nucleocapsid-specific antibodies often become undetectable within the first year following infection which is likely to lead to marked underestimation of the true proportion of those with prior infection. Since natural infection may act to boost vaccine responses, better assays to identify natural infection should be developed. Funding UK Government Department of Health and Social Care.