Findings of the present study in light of current publications
on residents with prior COVID-19
Three weeks after a single dose of BNT162b2 vaccine, residents with an
older infection were less often seropositive for N-protein IgG than
those with a newer infection (61.1 % vs 85.7 %). This result accords
with the time-related decline of natural SARS-CoV-2 antibodies observed
not only in the general population with prior COVID-1924 but also in NHs: a study showed that 91% of
residents were still seropositive for N-protein 6 months after COVID-19,
but with a decreasing antibody titer over time 25. The
rapid decay of N-protein IgG in the 90 days after mild COVID-19
infection has suggested a short-lasting humoral immunity against
SARS-CoV-2 26. The present study is quite reassuring
as it indicates a natural immunity in 61% of NH residents 9 to 12
months after infection, which is in line with the results shown after
other acute viral infections 27,28.
This study shows a link between N-protein IgG and S-protein IgG levels
after the first jab. RT-PCR-positive residents who were seropositive for
N-protein IgG more often exhibited a high S-protein IgG level after
vaccination (over 96% of them) than seronegative residents with a
positive RT-PCR from an older (80%) or newer (28.6%) infection. This
result is in line with influenza for which pre-existing immunity in
older individuals, contrary to immune-senescence or poor functional
status, is a strong correlate of post-vaccination immunity29,30.
It is reassuring to note that 80% of the RT-PCR-positive residents with
an older infection but who do not have a persistent humoral immunity
exhibit a high S-protein IgG level after the vaccine. This result
suggests a long-term persistence of previously-generated memory B cells
that can induce a rapid clonal expansion and terminal differentiation to
produce high affinity anti-S-protein IgG after the vaccine31, as observed for common viruses32. In line with this hypothesis, a robust boosting
after the first mRNA jab was found to strongly correlate with levels of
pre-existing memory B cells in recovered individuals, identifying a key
role for memory B cells in recall responses to SARS-CoV-2 antigens33. Taken together, these results suggest that both
natural humoral immunity (that appears to decrease over time) and
cellular immunity (that seems to be maintained over time) may modulate
the high level of SARS-CoV-2 S-protein IgG following a single BNT162b2
jab in nursing home residents having recovered from COVID-19. This
highlights the utility of defining cellular responses in addition to
serologies to predict the immune response to vaccine in this population.
This result may be important since the role of pre-existing immunity was
underscored during the 2009 A (H1N1)
pandemic, when older adults were less severely affected than younger
individuals 34.
The present study shows that NH residents with prior COVID-19 achieve
much higher S-protein IgG levels after one single jab than in younger
COVID-19 convalescents 35. It remains to be determined
whether vaccinated residents with prior COVID-19 (with at least one jab)
will be better protected against reinfection during outbreaks in NHs
than unvaccinated residents with prior COVID-19 4.
The persistence of N-protein IgG in 85.7% of residents with a newer
infection (in the past 3 to 7 months) and the increase in S-protein
level observed with increasing time between COVID-19 and vaccination
both support the hypothesis that, in most residents, the vaccine should
be administered at least 3 months after COVID-19 infection, even if
reinfection is possible within those 3 months 36.