Durable antibody responses in staff at two long-term care facilities, during and post SARS-CoV-2 outbreaks
SARS-CoV-2 has had a disproportionate impact on non-hospital healthcare settings such as long-term care facilities (LTCFs). The communal nature of these facilities, paired with the high-risk profile of residents, has resulted in thousands of infections and deaths and a high case fatality rate. To detect pre-symptomatic infections and identify infected workers, we performed weekly surveillance testing of staff at two LTCFs which revealed a large outbreak at one of the sites. We collected serum from staff members throughout the study and evaluated it for binding and neutralization to measure seroprevalence, seroconversion, and type and functionality of antibodies. At the site with very few incident infections, we detected that over 40% of the staff had preexisting SARS-CoV-2 neutralizing antibodies, suggesting prior exposure. At the outbreak site, we saw rapid seroconversion following infection. Neutralizing antibody levels were stable for many weeks following infection, suggesting a durable, long-lived response. Receptor-binding domain antibodies and neutralizing antibodies were strongly correlated. The site with high seroprevalence among staff had two unique introductions of SARS-CoV-2 into the facility through seronegative infected staff during the period of study but these did not result in workplace spread or outbreaks. Together our results reveal that high seroprevalence rate among staff can contribute to herd immunity within a workplace and protect against subsequent infection and spread within a facility.