According to The Lancet study, a third dose of COVID-19 vaccine reduces severe disease outcomes compared to people who received two doses at least five months ago. Researchers from the Clalit Research Institute and Harvard University conducted the study in Israel, a world leader in third-dose COVID-19 vaccination rates.
The study is the first to assess the effectiveness of a third dose of Pfizer-BioNTech’s mRNA COVID-19 vaccine against severe outcomes with adjustment for comorbidities and behavioral factors
Researchers at BioNTech conducted a recent clinical trial with a smaller sample size and did not estimate the third-dose’s effects on more severe outcomes.
From July 30 to September 23, 2021, the study occurred during Israel’s fourth wave of Coronavirus infection and illness, during which the Delta variant was the dominant strain in the country for most new infections. 728,321 individuals aged 12 or older who received the third dose of the Pfizer vaccine were reviewed by researchers.
The individuals in this study were carefully matched 1:1 with 728,321 individuals who received only two shots of the Pfizer vaccine at least five months earlier. Individuals were dynamically assigned to each group based on their changing vaccination status.
The results reveal that, compared with individuals who received only two vaccine doses five months prior, those who got three doses had 93 per cent lower risk of COVID-19-related hospitalization, 92 per cent lower risk of severe disease, and 81 per cent lower risk of death. Vaccine effectiveness was found to be similar for different sexes, age groups and number of comorbidities, the researchers said.
The study also included a population-level analysis which found that infection rates began to drop for each age group 7-10 days after they became eligible for the third dose.
According to Professor Ran Balicer, senior author at Clalit Research Institute in Israel, “These results suggest that the third dose of the vaccine is highly effective against severe COVID-19-related outcomes among different age groups and population subgroups, one week after the third dose.”
According to Harvard Medical School professor Ben Reis, a lack of information about the vaccine’s effectiveness has been a major driver of vaccine hesitancy.
This study provides reliable information on third-dose vaccine effectiveness, which may be useful to those who have not yet decided about vaccination with a third dose, said Dr. Reis. Prof. Miguel Hernan from the Harvard T.H. Chan School of Public Health said the trial of the Pfizer vaccine provided compelling evidence that it prevents symptomatic infection, but the estimates for severe disease and specific age groups were too imprecise