Are we seeing immunity waning in Israel? The MoH shared some raw data, and together with @geller_mic we tried to get a qualitative answer to this question. TL;DR – it seems that there is immunity waning, increasing risk of infection of early vaccinated by ~80%. ==>
Several remarks before we start:
1. This is a qualitative analysis. We don’t have data on individuals, only very limited information shared by the MoH.
2. We are talking about immunity waning, not vaccine effectiveness. Delta may affect VE, but data here is independent of that
1. This is a qualitative analysis. We don’t have data on individuals, only very limited information shared by the MoH.
2. We are talking about immunity waning, not vaccine effectiveness. Delta may affect VE, but data here is independent of that
3. The analysis below is on the risk of infection, not severe disease. I wrote about VE of severe disease in a different thread.
4. This is twitter science, take it as it is. There are many assumptions and caveats to this analysis.
4. This is twitter science, take it as it is. There are many assumptions and caveats to this analysis.
https://twitter.com/dvir_a/status/1416867665247887365
After we cleared the table, let's dive into the data. By the end of January ~1.8 million Israeli already received their second dose. Below is data of confirmed cases in this cohort (left >60+, right 16-59). 
Let’s start with the younger group, about 770K individuals. It says 16 and older, but almost all are 20+. In the week of July 4-10 there were 350 cases. In all of the vaccinated population in this age group there were 1056 cases (33%), so 706 cases in “late” vaccinated.
The problem is that it's not clear what proportion of the population was vaccinated early. 770K is 18%, but this is problematic. It includes non-vaccinated, ultra-orthodox and Arab citizens (the current wave has not spread to those groups yet).
We looked at how many were vaccinated in “general” pop cities, and we estimate it at about 22%. If this is the background that we need to compare to, it means that early vaccinated are at ~75% higher risk for infection. If VE is ~90%, after half a year it drops to ~82.5%.
An explanation on the calculation: based on those numbers our expectation in early group is = 706 cases * 0.22/0.78 ~= 200 --> 350/200 = 1.75
Now to adults. Here we have 370 cases in early vaccinated from 421 total (88%). What is the expected rate? We estimate it at about 79% of 60+ in the general population. This translates to about a factor of 2 in risk, or if VE is 90% then after half a year later it drops to 80%.
We also looked at the week of July 11-17. The results from that week are more or less the same. This brings us to about 80% increased risk for early vaccinated vs. late vaccinated in both age groups.
Delta might affect VE, but it's very hard to estimate it based on Israeli data. The data suggest that non-vaccinated adult individuals are reluctant to get tested, which skews calculations towards very low levels of VE.
I personally think that Delta VE is still around 90% for infection, but we will have to wait for better studies. Our analysis does show that after half a year or so this 90% drops to around 82%. It’s a significant reduction, but not a game-changer.
Note that we are comparing here vaccinated individuals to vaccinated individuals. It still might be that “late” vaccinated individuals tend to get tested at lower rates or other biases we can’t assess here.
In conclusion, we are seeing immunity waning. It's disturbing on its own, however it is likely that the vaccine is still working quite well. More rigorous research is required to confirmed our estimates.
and now from the MoH released their analyses.
https://twitter.com/Nadav_Eyal/status/1417923435737534467
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