UPDATE:   The news article misreports the results, probably because the lab itself communicates so poorly (you have to skip all the way down to #6 in the tweet thread for the point to finally be made clear).  In fact, there were no cases of infection by the South African variant two weeks after the second dose!  The variant did better than expected at infecting people before that time.  So, in fact, once fully faccinated, Pfizer is highly protective even against the South African variant!  Both the journalists and the lab deserve the blame here for poor communication of the results.  (Thanks to Matthew Noah Smith for calling my attention to this.)

Although how much less effective we still don't know:

A team from Tel Aviv University and the Clalit healthcare organization sequenced the swabs of 150 Israelis who tested positive for COVID-19 despite having been vaccinated.

In their study, the prevalence of the South African strain among vaccinated individuals who were infected despite their inoculation was eight times higher than its prevalence in the unvaccinated infected population. Though the number of such infections among the vaccinated was relatively small, the findings indicated that this variant was far more successful in getting through vaccinated individuals’ defenses than other strains.

“Based on patterns in the general population, we would have expected just one case of the South African variant, but we saw eight,” Prof. Adi Stern, who headed the research, told The Times of Israel….

The research, which has been posted online but not yet peer-reviewed, is likely to raise questions about Pfizer’s own real-world study, which found that in South Africa, despite the local strain being prevalent, the vaccine was 100 percent effective.

The Tel Aviv research appears to corroborate a recent study from Ben-Gurion University of the Negev, which found that the vaccine response is less effective against the South African variant. It drew its conclusion by analyzing blood samples, while the new research is based on actual sequenced test results.

Stern emphasized that the South African variant remains uncommon within the vaccinated population, and stressed that the study does not precisely indicate the level of protection against the variant, because its prevalence in Israel is very low – about 1% of all cases.

The study also examined the so-called British variant’s ability to break through the vaccine’s defenses, compared to the original strain. No difference was found in the UK variant’s ability to infect fully vaccinated individuals (after two doses). However, it was more able to infect partially vaccinated individuals than the original.

It would also be useful to know how sick those who were infected with the South African variant got; even if the vaccine didn't prevent infection quite as well, perhaps it still prevented serious illness?