A surge involving the rapidly-transmitting Delta variant in heavily vaccinated countries has led to much hand-wringing that the vaccines are not effective against Delta, or vaccine effectivenss wanes after 4-6 months. This has fueled anti-vaccine sentiment suggesting the vaccines are not working, and causing much stress in vaccinated people that they are not as protected as they thought they would be.

In this post, I will focus on vaccine effectiveness vs. severe disease/hospitalization, which is the key factor for public health. I will not deal with vaccine effectiveness vs. symptomatic or asymptomatic disease here -- that has its own set of nuances that I will save for a future post.