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Incidence of SARS-CoV-2 infection according to baseline antibody status in staff and residents of 100 Long Term Care Facilities (VIVALDI study)

By Maria Krutikov, Tom Palmer, Gokhan Tut, Chris Fuller, Madhumita Shrotri, Haydn Williams, Daniel Davies, Aidan Irwin-Singer, James Robson, Andrew Hayward, Paul Moss, Andrew Copas, Laura Shallcross

Posted 10 Mar 2021
medRxiv DOI: 10.1101/2021.03.08.21253110

Background SARS-CoV-2 infection represents a major challenge for Long Term Care Facilities (LTCFs) and many residents and staff are now sero-positive following persistent outbreaks. We investigated the relationship between the presence of SARS-CoV-2 specific antibodies and subsequent infection in this population. Methods Prospective cohort study of infection in staff and residents in 100 LTCFs in England between October 2020 and February 2021. Blood samples were collected at baseline (June 2020), 2 and 4 months and tested for IgG antibodies to nucleocapsid and spike protein. PCR testing for SARS-CoV-2 was undertaken weekly in staff and monthly in residents. The primary analysis estimated the relative hazard of a PCR-positive test by baseline antibody status, from Cox regression adjusted for age and gender, and stratified by LTCF. Findings Study inclusion criteria were met by 682 residents and 1429 staff. Baseline IgG antibodies to nucleocapsid were detected in 226 residents (33%) and 408 staff (29%). A total of 93 antibody-negative residents had a PCR-positive test (0.054 per month at risk) compared to 4 antibody-positive residents (0.007 per month at risk). There were 111 PCR-positive tests in antibody-negative staff (0.042 per month at risk) compared to 10 in antibody-positive staff (0.009 per month at risk). The adjusted hazard ratios for reinfection in staff and residents with a baseline positive versus negative antibody test were 0.13 (95% CI 0.05-0.40) and 0.39 ((95% CI: 0.19-0.77) respectively. Of 12 reinfected participants with data on symptoms, 11 were symptomatic. Antibody titres to spike and nucleocapsid were comparable in PCR-positive and PCR-negative cases. Interpretation The presence of IgG antibodies to nucleocapsid was associated with substantially reduced risk of reinfection in staff and residents for up to 10 months after primary infection. Funding UK Government Department of Health and Social Care

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