Prior Covid-19 and high RBD-IgG levels correlate with protection against VOC-delta SARS-CoV-2 infection in vaccinated Nursing Home Residents

Blain, H.; TUAILLON, E.; Pisoni, A.; Soriteau, L.; Million, E.; Leglise, M.-S.; Bussereau, I.; Miot, S.; Rolland, Y.; Picot, M.-C.; Bousquet, J. J.

Background Nursing Home (NH) residents are at high risk of serious illness and death from coronavirus disease 2019 (Covid-19), especially with the SARS-CoV-2 variants of concerns (VOC). It is unknown as to whether a history of Covid-19 prior to the vaccine and post-vaccine RBD-IgG levels are predictors of BNT162b2 vaccine effectiveness against VOC-delta in nursing home residents. Methods We analyzed the data from two NHs that faced a VOC-delta outbreak in July-August 2021. These NHs had suffered prior Covid-19 outbreaks in 2020 and 2021. In many of the residents, RBD-IgG levels were measured 6 weeks after the second vaccine dose, i.e. 3 to 5 months before the VOC-delta outbreak onset, and again during the outbreak (SARS-CoV-2 IgG II Quant assay, Abbott Diagnostics). We compared residents with vs without prior Covid-19 for (i) VOC-delta incidence, (ii) the correlation between post-vaccine RBD-IgG levels and VOC-delta incidence, and (iii) the time-related change in RBD-IgG levels. Results Among the 140 analyzed residents (58 to 101 years; 94 females, 46 men, mean age (SD): 84.6 yr (9.5 yr), one resident among the 44 with prior Covid-19 before vaccination developed a VOC-delta infection during the outbreak (1.3%) vs 55 of the 96 without Covid-19 prior to vaccination (57.3 %)(p<0.0001). The median value for RBD-IgG after the vaccine and during the outbreak was higher in residents with prior Covid-19 (31553 AU/mL and 22880 AU/mL) than in those without (1050 AU/mL and 260 AU/mL)(p<0.0001). In residents without Covid-19 prior to vaccination, post-vaccination RDB-IgG levels did not predict protection against VOC-delta infection. Conclusions In contrary to residents with prior SARS-CoV-2 infection, those without a history of Covid-19 before two BNT162b2 doses are not protected against VOC-delta infection and their RBD-Ig-G levels are low 3 to 5 months after vaccination. This suggests that a booster vaccine dose should be considered in this group of residents for a better protection against VOC-delta infection.