An interesting article published by Jabbal and others in Eurosurveillance, Europe’s journal on infectious disease surveillance, epidemiology, prevention and control looked at whether a single dose of the Pfizer vaccine was effective.
They found that a single dose was immunogenic in the vast majority, 92%, of their study cohort 21 days post vaccination, and this included 92% of people who had no history of COVID-19 infection.
There were 39 healthcare workers who did not respond to the first dose of the vaccine as they were older with a mean age of 57 than those who did with the mean age of 45.
Amongst those with antibodies after vaccination, IgG titres decreased with increasing age, although the authors noted that the decrease was small and of unclear clinical significance.
They found that vaccinating individuals with evidence of prior COVID-19 infection led to a boost response achieving IgG titres approximately one order of magnitude higher than those with no previous infection.
Interestingly, this was the case in the cohort regardless of whether SARS-CoV-2 antibodies were detectable or not immediately before vaccination and regardless of the time interval between infection and vaccination.
Although these results were based on small numbers, this provides reassurance that the well documented, rapid waning of IgG antibodies post COVID-19 infection does not necessarily translate to the loss of immunity.
This boost like response seen amongst previously infected individuals in the cohort suggested that B-cell mediated memory immunity is preserved regardless of IgG status.
Their study confirmed recently published evidence suggesting that immune memory persists for at least six months post infection.
The boost like response seen among previously infected individuals in the cohort suggested that B-cell mediated memory immunity was preserved regardless of IgG status.
This study confirmed recently published evidence suggesting that immune memory persists for at least six months post-infection.
One single case in the cohort showed a boost type response persisting almost 10 months after testing positive by PCR, suggesting that this could even be longer.
The studies suggested that in situations of vaccine scarcity, it may therefore be possible to assume that most individuals with prior evidence of infection are not prioritised for vaccination regardless of pre-vaccination IgG levels.
Nevertheless, infection does not protect 100% against reinfection and offering a vaccination to those individuals may confer additional protection.
A single dose of vaccine in these individuals seems to boost the response although the optimal timing between infection and vaccination as well as the ensuing duration of protection remains to be determined.
Dr Paul Ettlinger
BM, DRCOG, FRCGP, FRIPH, DOccMed