How effective has the COVID-19 vaccination program been in Israel?

Using publicly available data on coronavirus disease 2019 (COVID-19) in Israel, a study suggests that the BioNTech-Pfizer BNT162b2 vaccine is proving extremely effective in the real world.

Several vaccines have now been approved for COVID-19 and many countries have started intensive vaccination programs. In Israel, vaccination began on December 20, 2020. By the end of January, 33% of the population had received the first dose of BioNTech-Pfizer vaccine, also known as BNT162b2, and 19% had received the second dose.

As vaccinations began, the country was in the midst of a third wave of COVID-19, with more than double cases and hospitalizations by mid-January 2021. In response, the country declared a blockade on January 8, 2021. But the cases did not decrease and there were questions about the effectiveness of the vaccine.

However, it is difficult to estimate how effective vaccines are in the real world. Vaccination uptake is linked to the socio-economy and demographics of a population, along with disparities between groups in terms of infection rates. Such confounders are not present in randomized clinical trials due to blindness. In the real world, individual clinical and demographic data are needed to determine the effectiveness of the vaccine.

Estimation of vaccine efficacy

In a paper published on medRxiv * The preprint server, Assistant Professor Dvir Aran of the Technion-Israel Institute of Technology, used publicly available data on COVID-19 cases and hospitalization after vaccination with the Pfizer vaccine. The author provides estimates of the effectiveness of vaccines in reducing cases.

The author used daily positive case data and hospitalization data from the Israeli database of the Israeli Ministry of Health COVID-19, including hospitalization after vaccination until January 31, counted the number of people vaccinated each day and multiplied it by the rate daily population, adjusting for the difference in the number of cases between the vaccinated and the general population. Using these parameters, the author estimated the effectiveness of the vaccine.

The analysis found that there were 3,082,190 people who were vaccinated with a first dose between December 20, 2020 and January 31, 2021, and 1,789,836 had also received the second dose. Of the total vaccinated, 1,215,797 were over 60 years old.

Of those vaccinated, 31,810 tested positive for SARS-CoV-2 and 1,525 were hospitalized or died. The analysis indicates a reduction of approximately 28% in the number of cases for those over 60 years of age by day 13 after the first dose, a reduction of 43% between days 14 and 21 and a reduction of over 80% after the second dose.

This analysis is based on the assumption that all people who received their vaccines in time had the same level of positive cases as the general population. But this is not true in the real world. Older people have lower positivity, and lower socio-economic groups have higher positivity rates.

Adjusting for this, the author found that if it is assumed that the vaccinated population has half the number of cases as the general population, there is no decrease in the number of cases until 21 days after the first dose. The number of cases decreased by 66% seven days after the second dose.

For people over the age of 60, which is a major proportion of seriously ill cases, the analysis suggests a strong effect of the vaccine, reducing severe cases by about 60% after the first dose and up to 94% seven days after the second dose.

Extremely effective vaccine in the real world

Overall, the analysis suggests a reduction in positive cases of 66-83% in people over 60, 76-85% for those under 60 and 87-96% effective in preventing severe cases.

The Pfizer vaccine has been reported to be 95% effective one week after the second dose, based on clinical trials, although the efficacy before this is unclear. Analysis of real-world data from Israel, which includes approximately 140 times more individuals than the study, provides an estimate of the vaccine’s effectiveness in reducing cases and disease severity.

The author acknowledges some limitations of the analysis. These include delays in reporting cases, the fact that hospitalization may increase the number of cases observed, and limitations on making inference at the individual level as an analysis used to aggregate the number. As the incidence in the general population is also affected by vaccination, the actual effectiveness may be higher. The author writes that the analysis provides “strong assurance” that the vaccine is extremely effective.

*Important Note

medRxiv publishes preliminary scientific reports that are not evaluated by colleagues and therefore should not be considered conclusive, guide clinical practice / health-related behavior or be treated as established information.