The study, released on April 10, 2021, was published as a draft on medRvix.com and has not been peer-reviewed.
The Pfizer/BioNtech BNT162b2 mRNA vaccine has proven to be highly effective in its protection levels, however, there is still some apprehension that several variants of concerns (VOCs) can overcome the immune defenses generated by the vaccines, according to the research paper.
The case-control study examined whether BNT162b2 vaccinees with documented SARS-CoV-2 infection were more likely to become infected with B.1.1.7 or B.1.351 compared with unvaccinated individuals.
To this end, 400 people who had tested positive for COVID-19, 14 or more days after they received one or two doses of the vaccine, were compared with 400 unvaccinated patients with the disease. Researchers matched age, gender, and other characteristics in the two groups, according to Reuters.
The scientists found that the B.1.351 variant made up about 1.0 percent of all the COVID-19 cases across the two groups. However, among patients who had received two doses of the vaccine, the variant’s prevalence rate was eight times higher than those unvaccinated – 5.4 percent versus 0.7 percent.
This observation suggests the Pfizer vaccine may be less effective against the South African variant, compared to the original COVID-19 or UK variant.
“We found a disproportionately higher rate of the South African variant among people vaccinated with a second dose, compared to the unvaccinated group. This means that the South African variant is able, to some extent, to break through the vaccine’s protection,” said Tel Aviv University’s Adi Stern, reports US News.
The research comes with a note of caution – One being the study only had a small sample size of people infected with the South African variant because of its rarity in Israel. Secondly, the research was not intended to deduce overall vaccine effectiveness against any variant, since it only looked at people who had already tested positive for COVID-19, not at overall infection rates.
Pfizer/BioNtech said on April 1 that their vaccine was around 91 percent effective at preventing COVID-19, citing updated trial data that included participants inoculated for up to six months.
As for the South African variant, The companies say that among a group of 800 study volunteers in South Africa, where B.1.351 is widespread, there were nine cases of COVID-19, all of which occurred among participants who got the placebo. Of those nine cases, six were among individuals infected with the South African variant.
“Even if the South African variant does break through the vaccine’s protection, it has not spread widely through the population,” said Stern, adding that the British variant may be “blocking” the spread of the South African strain.