Thread by @ofraam

A new pre-print of a study showing a detailed analysis of waning immunity in Israel: tinyurl.com/WaningCOVID19
TL/DR: infection rate and severe disease rates both significantly increase with vaccine age (thread)

The study analyzed data on all PCR positive test results between July 11-31 in Israel, a period of a major covid (Delta variant) outbreak and compared infection rates and severe outcomes between individuals who were vaccinated in different time periods.

The rates of infection show a significant decrease in protection with vaccine age. Results hold when controlling for the different age groups and high-risk populations who vaccinated earlier (white bars - periods at which only people at higher risk were eligible for vaccination.

A similar trend is observed for severe outcomes. E.g., 60+ y/o who received their 2nd dose in March were 1.6 (CI: [1.3, 2]) times more protected against infection and 1.7 (CI: [1.0, 2.7]) times more protected against severe COVID-19 compared to those who received it in January

One of the major sources for this new outbreak were people who traveled abroad and returned infected to Israel. This is important because this group is not representative of the general Israeli population and might be biased to vaccinate early (higher socio-economic status, etc.)

To control for this, these people were removed from the analysis (results still hold if they are added). It is also still unknown what happens to the protection of people who recovered from COVID, therefore people who are known to have had COVID previously were also removed

Another potential bias is that some people are more likely to follow recommendations and get tested (possibly those who also vaccinated early). To account for this, the analysis was adjusted for the # of PCR tests taken before the vaccination campaign (no past PCR, 1 test, >2).

Yet another potential bias might be demographic groups that differ in their compliance with medical recommendations and vaccination rates, therefore the analysis also took into account the major demographic groups

Finally, during the analyzed period, infections grew exponentially, further affecting the likelihood of getting infected. The analysis was also adjusted to account for the rate of infection on each particular day

Given some responses, let me note that the vaccine is still effective in the sense that infection and severe rates are much lower than for the unvaccinated population. The study shows decline with vaccine age comparing people who vaccinated early to people who vaccinated later

And also worth mentioning preliminary encouraging findings with respect to the booster, see here:

https://twitter.com/yuvharpaz/status/1428426246430597121

Clarification: the study was done by my colleague @YairGoldberg1 at @TechnionLive (who is not active here) and a group of researchers from the Gertner Institute, @IsraelMOH, Hebrew university, Weizmann Institute, Tel Aviv University and Ben Gurion University

Since people are asking about the comparison to unvaccinated, this can be found in the supplementary appendix, see the table here

This paper is now officially out on NEJM:
nejm.org/doi/full/10.10…