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).