Explanation About the Effectiveness of the Vaccine for Coronavirus in Israel

The Ministry of Health is continuously monitoring the effectiveness of the vaccine for coronavirus.

As published yesterday (5.7.2021) in the Ministry of Health's announcement, epidemiological analysis by the public health services in the Ministry of Health reveals that starting June 6th, the effectiveness of the vaccine decreased to 64% in preventing infection and 64% in preventing symptomatic illness.

This decrease was observed simultaneously with the spread of the Delta variant in Israel. Nevertheless, the effectiveness of the vaccine in preventing serious illness and hospitalization cases is estimated at 93%.

Explanation on the calculation of the vaccine's effectiveness

The calculation of the vaccine's effectiveness is based on occurrence per time-person comparing vaccinated and non-vaccinated individuals during the monitoring period. 

• When the vaccine has 100% effectiveness, there will not be a single case among all vaccinated individuals.
• When the vaccine has not effectiveness (0), the infection rate will be the same between vaccinated and non-vaccinated individuals.

The meaning of the vaccine effectiveness parameter is which percent of all infection cases (or hospitalizations or mortality) could be prevented by vaccination.

Data is calculated in a statistical model that allows for standardization into factors which may affect the results, such as the age of the infected individual and the week of outbreak. Detailed information is found in the study methods that were published in the Lancet Journal. 

People confirmed as coronavirus patients before the beginning of the monitoring period are removed from the analysis, since their chances of repeated infection are different from those of the rest of the population who has yet to be infected for the first time. effectiveness is measured in those aged 16 and older, due to lack of data on vaccinated individuals aged 12 to 15 to allow for this calculation. In the attachment below there are tables with infection rate data according to monitoring period that serve as basis for the Ministry of Health's calculations, as well as the full calculation formula.

The following data is currently being calculated: Infection, symptomatic illness (with fever and/or respiratory symptoms), serious illness and hospitalization cases.