Design of the study
Between March and April 2021, among the 122 NHs (6 241 residents) followed by the Montpellier Covid-19 support platform after vaccination,20 13 had at least one RT-PCR-positive resident (747 residents; 124 positive RT-PCR residents). Among these 13 NH, a prospective cohort study was carried out in all seven NHs with more than five RT-PCR-positive residents tested at least 14 days after the end of the vaccination campaign, considering that the exposure risk of residents should be sufficient to study the effect of the vaccination on Covid-19 incidence. Clinical characteristics of all residents present at the time of the first positive RT-PCR were studied, regardless of the date of their arrival in the NH. As for other Occitanie NHs, when a first RT-PCR-positive resident was diagnosed, the same infection prevention and control (IPC) measures were implemented and no new resident entry was permitted until the end of the outbreak (Online supplement 1) 21,22. Blood was drawn on the day of positive RT-PCR testing in the first infected residents and within the 5 following days in all the others. Blood collection within this delay was possible in 6/7 NHs. Blood sample allowed to measure IgG-RBD and nucleoprotein IgG levels and, in RT-PCR-positive residents, N-Ag. Serum neutralizing antibodies were assessed in a subsample of 36 vaccinated residents from the first NH facing a SARS-CoV-2 outbreak, chosen to have a wide range of IgG-RBD values.
Participants
When a first resident had a positive RT-PCR, residents and their family or legal representative were informed of the possibility to assess RDB-IgG and nucleocapsid IgG in order to assess humoral immunity.
All residents of the 6 NH in which the blood sample was offered were tested, except those in palliative medical situation and those for whom informed consent for the blood collection and the use of anonymized data was not obtained. History of previous RT-PCR testing and the Charlson comorbidity index were determined based on residents’ medical files.23
The study was approved by the Montpellier University Hospital institutional review board (IRB-MTP_2020_06_202000534 and IRB-MTP