E-Paper
Study: Efficacy of Pfizer shot wanes faster than Astra’s
The study by researchers of University of Oxford is based on the results of a survey by UK’s Office for National Statistics that carried out RT-PCR tests from December last year to this month on randomly selected households.
The effectiveness of the Pfizer-BioNTech coronavirus vaccine appears to decline faster than that of the Oxford-AstraZeneca jab, according to a new study involving over 350,000 people in the UK, which was published early on Thursday.
The study by researchers of University of Oxford is based on the results of a survey by UK’s Office for National Statistics that carried out RT-PCR tests from December last year to this month on randomly selected households.
“Two doses of Pfizer-BioNTech have greater initial effectiveness against new Covid-19 infections, but this declines faster compared with two doses of Oxford-AstraZeneca,” the researchers at Oxford University said. The team is not linked to the group that developed the vaccine. The same vaccine is used as Covishield in India, where it is the mainstay of the inoculation drive.
The study found that “the dynamics of immunity following second doses differed significantly” between Pfizer and AstraZeneca, according to the university’s Nuffield Department of Medicine.
Pfizer had “greater initial effectiveness” but saw “faster declines in protection against high viral burden and symptomatic infection”, when looking at a period of several months after full vaccination, although rates remained low for both jabs.
“Results suggest that after four to five months, effectiveness of these two vaccines would be similar,” the scientists added, while stressing that long-term effects need to be studied.
The study’s findings come as Israel is administering booster shots, after giving 58% of the population two shots of the Pfizer jab.
The United States is also set to offer booster vaccines to boost antibody levels following concerns over declining effectiveness of the Pfizer and Moderna vaccines, especially against new variants of the Sars-CoV-2 virus that causes Covid-19.
The Oxford research also found that protection was higher among those who had already been infected with the virus. It also confirmed that vaccines are less effective against Delta, which was first seen in India.
The researchers added that viral load in vaccinated people appeared to now be similar to those infected with the Delta variant, but unvaccinated. “Peak viral load now appears similar in infected vaccinated and unvaccinated individuals, with potential implications for onward transmission risk, given the strong association between peak Ct (a viral load proxy) and infectivity,” the report said.
But, they add, the degree to which this higher viral load in vaccinated people may translate to new infections was unclear, since much of the virus “may be non-viable in those vaccinated, and/or their viral loads may also decline faster as suggested by a recent study of patients hospitalised with Delta”.
“Nevertheless, there may be implications for any policies that assume a low risk of onward transmission from vaccinated individuals (for example, relating to self-isolation, travel), despite vaccines both still protecting against infection, thereby still reducing transmission overall,” they said.
Evidence of the waning efficacy rates are also likely to be taken into account by Indian experts, who are studying the need for a booster dose and when that should be advised for people. At least a dozen countries have begun or announced plans to give booster doses to their people, including most prominent Western countries.
