The Israeli study finding that Pfizer is only 39% effective against Delta calcualted that figure by dividing the covid surge in cities with high vaccination rates to the Israeli national average of people vaccinated. This is a bad comparison because you have to compare apples to apples, and the denominator of that study should have been the vaccination rate of people in cities.

Because vaccination rate is higher in Israeli cities than the national average, the study compared an accurate estimate of the number of cases to a gross undercount of the number of people vaccinated. As a result, the numerator was correct but the denominator was way too low, which resulted in an estimate of effectiveness that was way too low as well.

This wasn't hard to predict. Every other study around the world estimated the vaccine's effective against symptomatic COVID at ~80%, so any study that claims it's 39% should be seriously scrutinized. Now that that study has been scrutinized more, it clearly doesn't hold water and we should accept the null hypothesis of ~80%.

tl;dr: the vaccine keeps working, and the anti-vaxxers can stay wrong and stay mad.