Real-world Covid Vaccine Effectiveness: Clalit’s preliminary analysis demystified
Ran Balicer
Chief Innovation Officer & Deputy-DG at Clalit Health Services. Founding Director, Clalit Research Institute. BGU Professor. Charité Honorary Professor. Head, WHO Collab Center. Member, UN High-Level Advisory Body on AI.
I want to elucidate the preliminary data we made public 10 days ago. By now we have much better data and inferences, but until the publication is out, the previous interim analysis continues to draw much attention.
Thus - a short thread:
Outcome measured:
Proportion of PCR tests that were positive. These tests are routinely performed in Israel for multiple indications, including symptomatic illness, contact with known case, quarantine shortening etc). ~100k tests per day.
Analysis results:
Positivity rates remained relatively constant on days 1-12 following vaccination, and same for the unvaccinated. Yet on day 14 post-vaccine, a statistically significant drop of 33% in PCR positivity was witnessed in the vaccinated but not unvaccinated.
The decline was maintained in the next days post vaccination, at which point numbers became too small for statistical inference.
Note 1:
These results were preliminary, and released as such for use of local decision makers.
The visible decline and its timing were encouraging
Note 2:
Those who know the Pfizer/Biontech clinical trials can recognize the differences between this real-world data and the clinical trial:
* age: 60+ vs 16+
* outcome: composite infection (sympt & asympt) vs sympt only
* follow-up time: we could not account for full 21 days
Thus any inference re: implications on the potential of the Pfizer/Biontech vaccine to eventually achieve the same impact in real-life as was witnessed in the trial - is on the interpreter’s responsibility.
Same for the debate of the risk/benefit trade-off of a 1-dose protocol.
Updated analysis with full time horizon, multiple outcomes and careful methodology - to follow soon in peer-reviewed scientific publication, open for all.
Consumer and Market research - Innovative research platforms at Kalka Research
4 年??? ????????, ?? ????? ??????? ?????? ?? ????? ?????????
Head of Office at WHO European Centre for Primary Health Care
4 年So impressive.
Global Business, Partnerships & Operations | Gets Things Done | People & Tech
4 年2 factors impede, and will continue to do so, the academic value of Israeli results - variants and politics.
The control group of unvaccinated is a different population. In many parameters. Those are people that didn’t not want to get vaccinated. And even more importantly, they are less likely to get tested. It’s not a randomized study. It’s comparing apples and oranges. A better comparison would be infections in the same group, between days 1-7 (control-vaccine not effective yet) and days 14-21. There the reduction was similar to the Pfizer study of about 90%. The 33% decline in infections number is not representative.
World View Indo-Pacific
4 年What about the fact that israel is in lockdown at the moment. That would be accounting for a decrease too. Need to mention that