How effective is the COVID-19 vaccination program in Israel?

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

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

As soon as vaccinations began, the country was in the midst of a third wave of COVID-19, with cases and hospitalizations more than doubling in mid-January 2021. In response, the country declared a blockade on January 8, 2021. However, the cases did not decrease and doubts arose about the vaccine’s effectiveness.

However, it is challenging to estimate the effectiveness of vaccines in the real world. Vaccination acceptance is intertwined with a population’s socioeconomics and demography, along with disparities between groups in infection rates. These confounding factors are not present in randomized controlled trials because of blinding. In the real world, clinical and demographic data at the individual level are needed to determine the vaccine’s effectiveness.

Estimating vaccine effectiveness

In an article published in medRxiv * prepress 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 cases and hospitalization data from the Israeli Ministry of Health’s public database COVID-19, including hospitalization after vaccination until January 31, counted the number of individuals vaccinated each day and multiplied that by the rate of daily cases of the total population, adjusting for the difference in the number of cases between the vaccinated population 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 the first dose between December 20, 2020 and January 31, 2021, and 1,789,836 also received the second dose. Of the total vaccinated, 1,215,797 were over 60 years old.

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

This analysis is based on the assumption that all people who received their vaccines at the beginning had the same level of positive cases as the general population. But, this is not true in the real world. Elderly people have less positivity and smaller socioeconomic groups have higher rates of positivity.

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

For people over 60, who make up the majority of severe 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.

Estimates of the vaccination efficacy rate at different levels of beta values. Standard errors are in the shade.

Highly 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 is reported to be 95% effective one week after the second dose based on clinical trials, although the effectiveness before that is unclear. Analysis of Israel’s real-world data, which includes about 140 times as many individuals as the trial, provides an estimate of the vaccine’s effectiveness in reducing cases and the severity of the disease.

The author recognizes some limitations of the analysis. This includes delays in reporting cases, the fact that hospitalization can increase the count of observed cases and limitations in making inferences at the individual level such as the analysis used to aggregate counts. As the incidence in the general population is also affected by vaccination, the real effectiveness may be greater. The author writes that the analysis provides a “strong guarantee” that the vaccine is highly effective.

* Important news

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