Secondary outcomes
Covid-19 severity: Symptoms were those recorded in residents’ files by NH staff between 7 days before and 14 days after RT-PCR testing, according to previous studies 21,25 (Online supplement 3). Covid-19 was considered to be severe when residents had either (i) respiratory symptoms including shortness of breath, respiratory rate > 24/min, oxygen saturation < 90% or when oxygen therapy was used, or (ii) when they displayed other symptoms whose intensity was considered by the NH coordinating practitioner as sufficient to justify an hospitalization or an examination by the resident’s General Practitioner. Other symptomatic residents had mild symptoms.
SARS-CoV-2 RBD and Nucleoprotein immunoglobulin levels: RBD-IgG levels were measured using the SARS-CoV-2 IgG II Quant assay (Abbott Diagnostics). Results were expressed as arbitrary units per mL (AU/mL; positive threshold: 50 AU/mL; upper limit: 40,000 AU/mL). According to the manufacturer and to previous studies, a first threshold ≥ 1,050 AU/mL was considered as a significant response, 26 and a second one ≥ 4,160 AU/mL indicated a high neutralizing effect.27 Nucleoprotein IgG (N-IgG) levels were measured using the SARS-CoV-2 IgG assay (Abbott Diagnostics) (Online supplement 4).