Thread by @dvir_a

Vaccine impact in Israel: changing trends. Analysis thread with @AArgoetti.
From about a month and a half ago we are experiencing a new “Delta” burst. Cases are accumulating, and more and more severe patients are in the hospitals.

https://twitter.com/AArgoetti/status/1420057245971361802

You’ve probably seen reports from Israel on low vaccine effectiveness in this wave. Is it because of Delta? Waning immunity? We think the reason is mostly that we got the denominator wrong.

https://twitter.com/dvir_a/status/1417813556888735750

See this graph. Until mid-July, the number (normalized to group size) of severe cases in the 65+ group was more or less similar between vaccined and unvaccined. This seemed troubling. But in the last 10 days trends have changed,

and now there are almost 3 times more daily new unvaccined severe cases. Looking at this plot, it seems that the R in the vaccined group is very close to 1, but in the last 10 days its almost 4 in the unvaccined group. We think its as expected with no mitigations beyond vaccines.

So why does it look like there is no difference until mid-July? @AArgoetti looked at the trends of cases in cities stratified by their vaccination rates.

We can see that cities on the lower quartile had low number of cases until recently, but since mid-July, most cases are coming from those cities.

This is what we got wrong. This “wave” started from cities with high vaccination rate and couldn’t “find” unvaccined adults at risk. The denominator we need to use until mid-July is >95% vaccination rate and not the country’s average.

So to summarize, the vaccines are highly effective in preventing severe cases and probably also symptomatic diseases, even for those vaccinated early.

Just to correct one misconception from my thread - many of you understood that we think there is no waning immunity. This analysis does not reject the waning hypothesis, it just shows that the vaccines are still highly effective even with possible waning.