From a just published UK study:
We found an absolute reduction of one dose vaccine effectiveness against symptomatic disease with the B.1.617.2 variant of approximately 20% when compared to the B.1.1.7 variant. However, reductions in vaccine effectiveness after two doses were very small. This was the case for both the BNT162b2 and ChAdOx1 vaccines. Using a TNCC analysis, estimated vaccine effectiveness against symptomatic disease with B.1.617.2 for a single dose of either vaccine is approximately 33%, for two doses of BNT162b2 is approximately 88% and for two doses of ChAdOx1 is approximately 60%.
What this means:
1. One dose of vaccine is less effective against delta variant than against wildtype.
2. Differences in two doses of vaccine were negligible between wildtype and delta variant.
3. Single dose of vaccine was 33% effective for symptomatic disease for delta variant.
4. Two doses of BNT162b2 (Pfizer) vaccine was 88% effective against delta variant while ChAdOx1 (AstraZeneca) was only 60%.
Their conclusions:
Overall, we found high levels of vaccine effectiveness against symptomatic disease after two doses. These estimates were only modestly lower than vaccine effectiveness against the B.1.1.7 variant. It is likely that vaccine effectiveness against more severe disease outcomes will be greater. Our finding of reduced effectiveness after dose 1, would support maximising vaccine uptake with two doses among vulnerable groups in the context of circulation of B.1.617.2.
I've tried to look at the Israeli study that everyone is quoting, but I can't find an English translation and don't speak Hebrew. I generally don't trust popular press interpretations because I've found them to be frequently wrong. But I found this from
Nature, which I do trust:
The data also suggest that the time between doses of vaccine doesn’t affect vaccine effectiveness, and that people who have previously tested positive for COVID-19 as well as receiving two vaccine doses have the best protection against future infection.
The analysis focused on the 18–64 age group and didn’t look at hospitalizations or fatalities, points out Dvir Aran, a biomedical data scientist at Technion — Israel Institute of Technology in Haifa. “This study is about infection, not severe disease,” he says. The results back up observations from Israel, which vaccinated its population very early in the pandemic, he says. “We are seeing high levels of breakthrough [infections] in the population that was vaccinated early, and on the other hand, we are seeing robust protection in those vaccinated recently — especially in 12–15-year-olds.”
So, the answer is still, even if you've been infected you need to be vaccinated because infected+vaccinated provides superior protected to infected alone. And you need both shots.