Israeli Prime Minister Naftali Bennett receives a third shot of coronavirus disease (COVID-19) vaccine as Israel launches booster shots for over 40 year-olds in Kfar Saba, Israel August 20, 2021. REUTERS/Ronen Zvulun

The Pfizer/BioNTech booster vaccine shot has been found to be effective in protecting individuals against severe COVID-19-related hospitalization and death, compared to receiving only two doses at least five months ago, according to a study by Israel’s largest healthcare organization and Harvard University published in The Lancet.

The largest real-world study assessing the effect of a third vaccine dose showed that it lowers the chances of COVID-19-related hospitalization by 93%, severe disease by 92 percent and mortality by 81 percent, compared with receiving two doses at least five months prior.

The analysis — conducted by researchers from Clalit Health Services, which provides mandatory healthcare for over half of the Israeli population, and Harvard University — is based on data from 728,321 people aged 12 or above who had received the third dose of the BNT162b2 vaccine, versus the same number of vaccinated individuals with two vaccine doses administered five months or more prior.

“The extensive nationwide rollout of Israel’s third-dose ‘booster’ COVID-19 vaccination campaign provided the Clalit Research Institute with a unique opportunity to assess, through its rich and comprehensive digital datasets, the effectiveness of the third dose in a real-world setting against the less common but severe complications of COVID-19,”said Prof. Ran Balicer, Director of the Clalit Research Institute and senior author of the study. “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.”

Prof. Miguel Hernán at the Harvard T.H. Chan School of Public Health noted that the “analysis of Clalit’s high-quality database emulates the design of the original trial, uses its findings as a benchmark, and expands upon them to confirm the vaccine’s effectiveness in adolescents.”

“This combination of evidence from randomized trials and observational studies is a model for efficient medical research, something which is especially important in COVID times,” Hernán added.

The study was conducted from July 30 through Sept 23 this year, coinciding with Israel’s fourth wave of coronavirus infection and illness, and during a period in which the Delta variant was the dominant cause of new infections. Vaccine effectiveness was evaluated at least seven days after receipt of the third dose, compared with receiving only two doses at least five months prior. The study participants had a median age of 52 years, and 51 percent were female.

Prof. Balicer, who also serves as Chairman of Israel’s National Expert Advisory Team on COVID-19 response, suggested that the “data should facilitate informed policy decision-making” for countries, who are experiencing a resurgence of SARS-CoV-2 infections as vaccine effectiveness is waning and have not administered a third booster dose.

Prof. Ben Reis, Predictive Medicine Group Director at the Boston Children’s Hospital Computational Health Informatics Program and Harvard Medical School said that the “careful epidemiological study provides reliable information on third-dose vaccine effectiveness, which we hope will be helpful to those who have not yet decided about vaccination with a third dose.”