Antibody response after one and two jabs of the BNT162b2 vaccine in nursing home residents: The CONsort-19 study

Abstract

Background: The humoral immune response following COVID-19 vaccination in nursing home residents is poorly known. A longitudinal study compared levels of IgG antibodies against the spike protein (S-RBD IgG) (S-RDB protein IgG) after one and two BNT162b2/Pfizer jabs in residents with and without prior COVID-19.

Methods: In 22 French nursing homes, COVID-19 was diagnosed with real-time reverse-transcriptase polymerase chain reaction (RT-PCR) for SARS-CoV-2. Blood S-RDB-protein IgG and nucleocapsid (N) IgG protein (N-protein IgG) were measured 21-24 days after the first jab (1,004 residents) and 6 weeks after the second (820 residents).

Results: In 735 residents without prior COVID-19, 41.7% remained seronegative for S-RDB-protein IgG after the first jab vs. 2.1% of the 270 RT-PCR-positive residents (p < 0.001). After the second jab, 3% of the 586 residents without prior COVID-19 remained seronegative. However, 26.5% had low S-RDB-protein IgG levels (50-1050 UA/ml) vs. 6.4% of the 222 residents with prior COVID-19. Residents with an older infection (first wave), or with N-protein IgG at the time of vaccination, had the highest S-RDB-protein IgG levels. Residents with a prior COVID-19 infection had higher S-RDB-protein IgG levels after one jab than those without after two jabs.

Interpretation: A single vaccine jab is sufficient to reach a high humoral immune response in residents with prior COVID-19. Most residents without prior COVID-19 are seropositive for S-RDB-protein IgG after the second jab, but around 30% have low levels. Whether residents with no or low post-vaccine S-RDB protein IgG are at higher risk of symptomatic COVID-19 requires further analysis.

Keywords: BNT162b2/Pfizer vaccine; COVID-19; antibodies against SARS-CoV-2; nursing home; rRT-PCR.

FIGURE 1

Flow Diagram of the sample of residents from 22 nursing homes having faced a COVID‐19 outbreak between March and December 2020

FIGURE 2

Correlation between N‐ and S‐protein IgG depending on the time of the COVID‐19 infection, 3 weeks after the first jab. Legend: N‐protein IgG levels: positive value when ≥0.8 signal to cutoff ratio (vertical bars); S‐protein IgG levels: high values when ≥4160 arbitrary unit (AU)/ml (horizontal bar)