Tel Aviv University and Clalit Research Institute researchers have found that the South African variant of the COVID-19 virus is significantly more likely to break through the protective effect of two doses of the Pfizer vaccine compared to the British COVID-19 variant. Researchers say that the exact reduction in effectiveness cannot be accurately assessed from these data, but estimate that the vaccine remains protective against this variant. The South African variant has not spread widely and remains very rare in Israel.

Among the leaders of the study was Professor Adi Stern of the Shmunis School of Biomedicine and Cancer Research at TAU’s George S. Wise Faculty of Life Sciences. 

The researchers examined some 400 members of Clalit Health Services who tested positive for COVID-19 14 days or more after receiving the first dose of the Pfizer vaccine and 400 unvaccinated members of similar age, sector, gender, place of residence etc., who had lab-confirmed COVID-19 at the same time period. All viral samples underwent genetic sequencing, which identified a prevalence of less than 1%  of the South African variant among the overall cohort.

However, among individuals who had been infected after receiving two doses of the vaccine, the prevalence rate was eight times higher than the rate in the unvaccinated matched individuals. This means that the Pfizer vaccine, though highly protective, probably does not provide the same level of protection against the South African variant of the coronavirus.

The results indicate that the South African variant is capable, to some degree, of breaking through the vaccine’s defenses. At the same time, this ability is probably limited, because this variant’s prevalence in the overall population remains low.

The study also compared the ability of the British (B.1.1.7) variant and the original COVID-19 virus strain to break through the vaccine’s defenses. The data indicate that in fully-vaccinated individuals (at least one week after the second dose) no difference was detected between the rates of the two variants. However, in 250 partially-vaccinated individuals (from two weeks after the first dose to one week after the second dose), the rate of the British variant was disproportionally higher compared to unvaccinated persons.  This means that the vaccine is most effective against the British variant only after the second dose.

“We wanted to know whether the rate of these variants is higher among vaccinated compared to unvaccinated individuals, and unfortunately the answer is yes,” Professor Stern says. “We found a disproportionally 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.”

Prof. Stern emphasizes, however, that this variant remains uncommon within the vaccinated population. She explains that the study does not precisely indicate the level of protection against the South African variant because its prevalence in Israel remains extremely low – about 1% of all cases.

“Though our results may give cause for concern, the low prevalence is encouraging,” adds Professor Stern. “Even if the South African variant  break through the vaccine’s protection, it has not spread widely through the population — unlike the British variant, which currently accounts for a large proportion of COVID-19 cases in Israel. One possible explanation is that the extensive spread of the British variant is blocking the spread of the South African variant.”