RBD-IgG levels correlate with protection in residents facing SARS-CoV-2 B.1.1.7 Outbreaks

Blain, Hubert; Tuaillon, Edouard; Gamon, Lucie; Pisoni, Amandine; Miot, Stéphanie; Delpui, Valentin; Si-Mohamed, Nejm; Niel, Clémence; Rolland, Yves; Montes, Brigitte; Groc, Soraya; Rafasse, Sophia; Dupuy, Anne-Marie; Gros, Nathalie; Muriaux, Delphine; Picot, Marie-Christine; Bousquet, Jean

BACKGROUND: Limited information exists on nursing home (NH) residents regarding BNT162b2/Pfizer vaccine efficacy in preventing SARS-CoV-2 and severe COVID-19, and its association with post-vaccine humoral response. METHODS: 396 residents from seven NHs suffering a SARS-CoV-2 B.1.1.7 (VOC-α) outbreak at least 14 days after a vaccine campaign were repeatedly tested using SARS-CoV-2 real-time reverse-transcriptase polymerase chain reaction on nasopharyngeal swab test (RT-qPCR). SARS-CoV-2 Receptor-Binding Domain (RBD) of the S1 subunit (RBD-IgG) was measured in all residents. Nucleocapsid antigenemia (N-Ag) was measured in RT-qPCR-positive residents, and serum neutralizing antibodies in vaccinated residents from one NH. RESULTS: The incidence of positive RT-qPCR was lower in residents vaccinated by two doses (72/317; 22.7%) vs one dose (10/31; 32.3%) or non-vaccinated residents (21/48; 43.7%)(p<0.01). COVID-19-induced deaths were observed in 5 of the 48 non-vaccinated residents (10.4%), in 2 of the 31 who had received one dose (6.4%), and in 3 of the 317 (0.9%) who had received two doses (p=0.0007). Severe symptoms were more common in infected non-vaccinated residents (10/21; 47.6%) than in infected vaccinated residents (15/72; 21.0%)(p=0.002). Higher levels of RBD-IgG (n=325) were associated with a lower SARS-CoV-2 incidence. No in vitro serum neutralization activity was found for RBD-IgG levels below 1,050 AU/mL. RBD-IgG levels were inversely associated with N-Ag levels, found as a risk factor of severe COVID-19. CONCLUSIONS: Two BNT162b2/Pfizer doses are associated with a 48% reduction of SARS-CoV-2 incidence and a 91.3% reduction of death risk in residents from NHs facing a VOC-α outbreak. Post-vaccine RBD-IgG levels correlate with BNT162b2/Pfizer protection against SARS-CoV-2 B.1.1.7.