Abstract
Background: There is insufficient information on the humoral
immune response following COVID-19 vaccination in nursing home
residents. A longitudinal study compared SARS-CoV-2 spike IgG (S-protein
IgG) levels after one and two BNT162b2/Pfizer jabs in residents with and
without prior COVID-19.
Methods: Twenty-two French nursing homes were included.
COVID-19 had been diagnosed with real-time reverse-transcriptase
polymerase chain reaction (RT-PCR) for SARS-CoV-2. Blood S-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: Among the 735 residents without prior COVID-19, 41.7%
remained seronegative for S-protein IgG after the first jab vs 2.1% of
the 270 residents with a previous positive RT-PCR (p<0.001).
After the second jab, only 3% of the 586 residents without prior
COVID-19 remained seronegative. However, 26.5% of them had low
S-protein IgG levels (50-1050 UA/mL) vs 6.4% of the 222 residents with
prior COVID-19. Residents with old infection (first wave), or
seropositive for N-protein IgG at the time of vaccination, had the
highest S-protein IgG levels. Residents with a prior COVID-19 infection
had higher S-protein IgG levels after one dose than those without two
jabs.
Interpretation: A single vaccine jab is sufficient to reach
immunity in residents with prior COVID-19. Most residents without prior
COVID-19 are seropositive for S-protein IgG after the second jab, but
around 30% have low levels of S-protein IgG. Whether residents with no
or low post-vaccine immunity are at higher risk of symptomatic COVID-19
requires further analysis.
Key words: COVID-19, BNT162b2/Pfizer vaccine, nursing home,
rRT-PCR, antibodies against SARS-CoV-2