Last August, when the delta variant became the dominant infection strain, Israel, one of the countries with the
highest levels of vaccination in the world, faced a scary pandemic wave. The frighteningly increasing number of
infections was seen as the perfect storm to test the effectiveness of the mRNA BNT162b2 vaccine.
The new surge forced the government to use a booster shot to protect the most vulnerable age groups.
Starting from the August national surveillance data, we analysed the temporal effectiveness of vaccination
against severe infections in the Israeli over 60 population. The study shows that the two-dose vaccine still works
in preventing people from getting seriously sick but not with the same effectiveness observed in the first months of
2021. However, the observed temporal increase of the vaccine effectiveness in Israel, during August, suggests a
correlation with the increase of the population protected by the booster shot.


Keywords: Sars-CoV-2, Vaccine Effectiveness, Relative Risk, Booster Dose


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