Wanted to clear this up. First, please remember that vaccines are preventives and NOT cures. One can still contract the virus once vaccinated and as long as it prevents them from facing severe disease and worse, it is still doing what it is supposed to.
https://www.timesofisrael.com/real-world-israeli-data-shows-south-african-variant-better-at-bypassing-vaccine/

Secondly, what is important to know about this study is that most infections were from B.1.1.7, with only 8 cases being B.1.351. After two doses, extremely high effectiveness against B.1.1.7 took effect. While they observed reduced effectiveness against B.1.351, they also saw it

did not spread in Israel. In other words, B.1.1.7 is keeping B.1.351 “in check” which is what a lot of scientists predicted months ago when these variants came onto the scene. This is a good thing. Why? We know the vaccines are HIGHLY effective against B.1.1.7

and we have variant specific boosters against B.1.351 currently being tested. Thirdly, another important fact that’s not being pointed out is that researchers concluded that the reduced effectiveness against B.1.351 occurs only within a short window of time. Hence, there were

NO cases of B.1.351 14+ days post second dose. That’s vital. B.1.351 does not spread as efficiently and if anything we should take this as even more evidence that we need to continue increasing vaccination efforts. The study can be found here:
https://www.medrxiv.org/content/10.1101/2021.04.06.21254882v1

Please read this thread as it is pertinent to understand the study out of Israel concerning Pfizer’s vaccine.