Conclusions
Recent studies show that even if the vaccine is very effective in
reducing severe forms of COVID-19 in nursing home residents, the
vaccination, even complete, may not totally prevent the risk of
SARS-CoV-2 outbreaks in nursing homes (Blain et al., submitted).41
This present study supports the hypothesis that i ) most of the
residents having recovered from COVID-19 (with a diagnosis using RT-PCR
or N-protein IgG) may only require one single vaccine dose to achieve
peak antibody and memory B cell responses. ii ) However, the
second dose reduces the prevalence of residents with low S-protein IgG
levels (≤1050 AU/mL)(from 11.5% to 2.7%). iii ) For individuals
whose infection history is unknown, measuring S-protein IgG antibody
levels just before the second jab could be useful in determining whether
a second dose is required. iv ) Most of the individuals without
prior COVID-19 have a low level of S-protein IgG 3 weeks after the first
jab, further confirming the benefit to administer the second dose
without delay to boost the antibody response. After two doses, around
30% of residents without prior COVID-19 have a low level of S-protein
IgG. Whether these residents with low antibody response after the
complete vaccine regimen are at higher risk of symptomatic COVID-19 and
whether they may benefit from a third vaccine dose remains to be further
investigated.
Additional studies are required to demonstrate whether the measure of
S-protein IgG after the vaccination should help to personalise the
vaccine schedules and reduce secondary effects related to possible
reactogenicity 42. Further studies are necessary also
to determine whether the present results obtained in residents infected
by the natural strain of the virus may be replicated in residents
infected by the new variants 43,44.