INTRODUCTION
Nursing Home (NH) residents are at high risk of serious illness and death from coronavirus disease 2019 (Covid-19) 1. Vaccination is safe and effective in adults, but less documented in NH residents. 2-4 Vaccine monitoring is partly based on post-vaccine IgG response against SARS-CoV-2 Receptor-Binding Domain (RBD) of the S1 subunit (RBD-IgG). 5 Based on RBD-IgG levels, 6-8 it is recommended in France to administer one mRNA vaccine dose in adults with prior Covid-19 and a third dose in immunocompromized patients. The interest of a third vaccine dose also arises in NH residents without prior Covid-19.2,9,10,11 It remains however unclear as to whether blood levels are predictive of SARS-CoV-2 infection and Covid-19 severe symptoms.
The recent emergence of SARS-CoV-2 ‘variants of concern’ (VOC) has transformed the epidemic, 12 possibly because RBD-IgG produced by vaccinated individuals is less effective in binding and neutralizing in vitro VOCs than the “wild type” SARS-CoV-2.13,14-17
Between January and March 2021, all French NH residents, including those of the Occitanie region, were offered two BNT162b2/Pfizer doses at a three-week interval. Between March and April 2021, 7 NHs of the Montpellier area (Occitanie) faced a SARS-CoV-2 B.1.1.7 (VOC-α) outbreak after the vaccine campaign.
The primary aim of this study was to assess the incidence of positive SARS-CoV-2 real-time reverse-transcriptase polymerase chain reaction (RT-PCR) results according to the vaccination status. Secondary aims were to compare Covid-19-related deaths and RBD-IgG levels according to the vaccination status. Other secondary aims were to assess the links in RT-PCR-positive residents between symptom severity, blood RBD-IgG levels and SARS-CoV-2 nucleocapsid antigenemia (N-Ag). Exploratory objectives were to analyze the link between RBD-IgG levels and serum neutralization activity against VOC-α and SARS-CoV-2 wild-type in one NH, and the links between biological markers with Covid-19 severity in RT-PCR-positive residents (N-Ag, C-reactive protein, and glomerular filtration rate).18,19