The protection against Covid infection offered by the Pfizer vaccine falters within months of getting a second dose, two new studies have found, but protection against severe disease, hospitalisation and death still remains strong.
The studies bolster arguments that those who have been fully vaccinated must still ensure they take adequate protection against Covid-19 and point to the increasing role of booster shots administered to people six months after they get their first two jabs.
One of studies, carried out among 4,868 healthcare workers in Israel, showed that vaccine effectiveness among men, those who are 65 years of age or older and those who are immunosuppressed – having weaker immune systems – reduces six months after the second dose.
It showed that the levels of neutralising antibodies, that are the human immune system’s first line of defence against infection, correlated with protection against infections, reported CNN, citing the study.
The Israel study pointed to other published research and said the lowering of immunity granted by the vaccine was not characteristic to Covid vaccines, but was found to decrease in vaccines against other diseases as well.
“Published work about many vaccines, such as those against measles, mumps, and rubella, has shown a small decrease each year of 5 to 10 per cent in the neutralising antibody levels,” it said.
“We found that a significant and rapid decrease in humoral response to the BNT162b2 vaccine [the Pfizer and BioNTech SE vaccine] was observed within months after vaccination,” it added.
Researchers conducting the other study in Qatar found that the Pfizer’s vaccine protection against infection peaked in the first month after the second dose and then dipped “month by month, before reaching low levels five to seven months after the second dose”.
This meant “a large proportion of the vaccinated population” could lose protection against infection “in the coming months, perhaps increasing the potential for new epidemic waves”.
The study, however, also said the implications for infections among those vaccinated “remain to be clarified”, even as the risk against hospitalisations and death remained sturdy, at 90 per cent or higher, for six months after the second dose.
“BNT162b2-induced protection against hospitalisation and death persisted with hardly any waning for six months after the second dose,” the study said.
“Implications of these findings on infection transmission remain to be clarified, but vaccine breakthrough infections were found recently, in this same population, to be less infectious than primary infections in unvaccinated persons,” it added.
The study warns that Qatar and other countries which, like it, have administered a high number of vaccinations, could see citizens drop their guard after getting inoculated.
“Vaccinated persons presumably have a higher rate of social contact than unvaccinated persons and may also have lower adherence to safety measures,” it said.
“This behaviour could reduce real-world effectiveness of the vaccine as compared with its biologic effectiveness, possibly explaining the waning of protection,” it added.
Meanwhile, another study published in The Lancet journal on Monday reported somewhat similar findings over the effectiveness of the Pfizer vaccine.
It said immunity granted by the vaccines dropped to 47 per cent from 88 per cent six months after the second dose.
The study said the dip in effectiveness was not because of new emerging coronavirus variants, but instead resulted from waning efficacy, reported Reuters.
The research, however, matched the findings of the Qatar study over the effectiveness of the Pfizer vaccine in preventing hospitalisations, saying this protection remained at 90 per cent.