Early in the pandemic, New Jersey (NJ) long-term care facilities (LTCFs) witnessed severe COVID-19 illness. With limited surveillance to characterize the scope of infection, we estimated the prevalence of antibody to the SARS-CoV-2 nucleocapsid protein among residents and staff, to describe the epidemiology, and to measure antibody distribution by prior PCR/antigen status and symptomatology. 10 NJ LTCFs of 20 solicited with diverse geography and bed-capacities were visited between October 2020 and March 2021. A single serum was tested for total N-antibody (ELISA) by the state laboratory. Residents' demographics and clinical history were transcribed from the patient record. For staff, this information was solicited directly from employees, supplemented by prior PCR/antigen results from facilities. 62% of 332 residents and 46% of 661 staff tested N-antibody positive. In a multivariable logistic regression in residents, odds ratios for older age and admission prior before March 1, 2020 were significant. Among the staff, odds ratios for older age, ethnic-racial group, nursing-related job, and COVID-19 symptoms were significantly associated with N-antibody positivity. In a sub-analysis in five better record-keeping LTCFs, 90% of residents and 85% of staff with positive PCR/antigen results were seropositive for N-antibody, yet 25% of residents and 22% of staff were N-antibody positive but PCR/antigen and symptoms negative. The high rate of clinically unsuspected infections likely contributed to the spread. These findings argue for robust surveillance, regular screening of asymptomatic individuals, and vaccinating both residents and staff to abate the pandemic. The data also provide guidance to prevent future outbreaks.

Expanding a previous study of the immune response to SARS-CoV-2 in 10 New Jersey long-term care facilities (LTCFs) during the first wave of the pandemic, this study characterized the neutralizing antibody (NAb) response to infection and vaccination among residents and staff. Sera from the original study were tested using the semi-quantitative enzyme-linked immunosorbent cPass neutralization-antibody detection assay. Almost all residents (97.8%) and staff (98.1%) who were positive for IgG S antibody to the spike protein were positive for NAb. In non-vaccinated subjects with a history of infection (positive polymerase chain reaction (PCR) or antigen test), the distribution of mean intervals from infection to serology date was not significantly different for S antibody positives versus negatives. More than 80% of both were positive at 10 months. Similarly, the mean NAb titer for residents and staff was not associated with interval from PCR/antigen positive to serology date, F = 0.1.01, Pr > F = 0.4269 and F = 0.77, Pr > F = 0.6548 respectively. Titers remained high as the interval reached 10 months. In vaccinees who had no history of infection, the NAb titer was near the test maximum when the serum was drawn seven or more days after the second vaccine dose. In staff the mean NAb titer increased significantly as the vaccine number increased from one to two doses, F = 11.69, Pr > F < 0.0001. NAb titers to SARS-CoV-2 in residents and staff of LTCFs were consistently high 10 months after infection and after two doses of vaccine. Ongoing study is needed to determine whether this antibody provides protection as the virus continues to mutate.