The effect of mass vaccination on COVID-19 mortality in Israel

A team of scientists from Israel and the USA has recently examined the efficacy of coronavirus disease 2019 (COVID-19) vaccination in reducing the death risk among people aged 70 years and above. They observe that despite government-imparted relaxation on non-pharmaceutical control measures, the vaccine saved more lives than expected by individual-level vaccine efficacy. The study is currently available on the medRxiv* preprint server.

Background

In December 2020, Israel started mass vaccination campaigns against COVID-19 by deploying an mRNA-based BNT162b2 vaccine developed by Pfizer/BioNTech. However, despite rapidly vaccinating the adult population, the country could not reach the herd immunity threshold. Moreover, soon after the beginning of the vaccination campaign, the government ordered relaxation on non-pharmaceutical control measures (mask-wearing, social distancing, movement restrictions, workplace closure, lockdown, etc.).

Since the vaccination campaign initially prioritized only older adults and the vaccine acceptancy was not uniform among different ethnoreligious groups, there remained a concern whether the vaccine could elicit necessary protection to the total population.

In the current study, the scientists examined the population-level effectiveness of COVID-19 vaccination in Israel. Moreover, they have compared the real-world effectiveness to the models based on the proven vaccine efficacy.

Cases and deaths, before and during the study period

Cases and deaths, before and during the study period

Study design

The scientists estimated the number of deaths that occurred among people over 70 years during the period when at least 90% of the study population were vaccinated for less than seven months. The study was conducted before the introduction of the delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Israel. Specifically, they estimated actual deaths and projected deaths with or without vaccination among people aged over 70 years.

Important observations

During the study period, a total of 370 deaths occurred due to COVID-19 among people aged over 70 years. During the same period, 930 COVID-19-related deaths occurred in the total population.

Based on the vaccination rate and individual-level vaccine efficacy, the expected number of deaths from COVID-19 in the study population was estimated to be 408. Similarly, based on a hypothetical situation of no vaccination and relaxed control measures, the expected number of deaths in the study population was estimated to be 5120.

During the study period, a total of 1119 confirmed COVID-19 cases occurred in the study population. The distribution of cases and deaths remained similar across all age groups before and during the study period.

Study significance

The study findings reveal that the COVID-19 vaccine BNT162b2 has saved more lives than that expected by individual-level vaccine efficacy. In other words, vaccination of 90% of the older population is sufficient to reduce COVID-19-related mortality. Importantly, this reduction in mortality has been achieved even after government-imparted relaxation on control measures.

As mentioned by the scientists, the study does not include cases and deaths caused by the delta variant of SARS-CoV-2, which is more infectious, virulent, and vaccine-resistant than the previously circulating alpha variant. Thus, it remains unclear how many lives the vaccine could save from the more deadly delta infection.

Moreover, the study does not examine the long-term efficacy of vaccination. In this context, there is evidence suggesting that the efficacy of COVID-19 vaccines declines over time. Thus, the current study findings are not sufficient to answer whether the vaccine will remain effective over many years against newly emerging viral variants.

*Important Notice

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

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