Booster Doses Protect Against Delta Variant, Says Real-World Study

Source: Freepik

According to the largest real-world study, booster doses are 93% effective against delta variant hospitalizations and deaths.

The deadly delta variant has caused a resurgence of COVID-19 cases across the world. Experts blame the rise in cases on the variant’s greater transmissibility and waning immunity of COVID-19 vaccines. As a result, health officials are now advocating for a booster dose; especially, in immunocompromised individuals and those at risk of severe infection. But, as low-income countries struggle with vaccine shortages, many are left debating over the prevalent vaccine inequity. However, despite it all, many wealthy nations have already begun administering booster doses to their population.

Israel was one of the first countries to get its hands on the Pfizer vaccine. Later in July of this year, the country began administering a third vaccine dose to its fully vaccinated population. Researchers from the Clalit Research Institute and Harvard University then conducted a study assessing the effectiveness of the booster dose against delta variant. They recently published the results in The Lancet.

93% Lower Risk

The study included data from July to September of this year, which is when Israel faced a deadly fourth wave due to the delta variant. Researchers recruited more than 700,000 people who had received a Pfizer vaccine booster dose. They then compared them to a carefully matched group that had only received two shots of the Pfizer vaccine at least five months prior.

According to the results, the booster group had a 93% lower risk of hospitalization, 92% lower risk of severe infection, and 81% lower risk of death. Moreover, these results remained consistent across different sexes and age groups.

These results show convincingly that the third dose of the vaccine is highly effective against severe COVID-19-related outcomes in different age groups and population subgroups, one week after the third dose. These data should facilitate informed policy decision-making.

Prof. Ran Balicer, senior author

Although the study points to the effectiveness of booster doses, the debate over vaccine inequity remains undiscussed.


Barda, N., Dagan, N., Cohen, C., Hernán, M. A., Lipsitch, M., Kohane, I. S., Reis, B. Y., & Balicer, R. D. (2021). Effectiveness of a third dose of the BNT162b2 mrna COVID-19 vaccine for preventing severe outcomes in Israel: An observational study. The Lancet.


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