The largest third-dose Covid-19 vaccine effectiveness study to date, conducted by Israel’s Clalit Research Institute, showed that the third-dose Pfizer / BioNTech vaccine reduced Covid-19-related hospitalizations by 93%; severe disease status in 92%; and deaths in 81%, compared to just two doses received at least five months earlier.
The research was published in the scientific journal The Lancet on Friday (29).
The study suggests that a third dose of vaccine is effective in reducing serious Covid-19-related outcomes compared to individuals who received two doses of vaccine at least 5 months ago.
The study is the first to estimate the efficacy of a third dose of a Covid-19 mRNA vaccine against severe outcomes with adjustment for several factors including comorbidities and behavioral factors.
The main study, conducted in collaboration with researchers at Harvard University, examined data from 728,321 people in Israel who received a third dose of the Pfizer/BioNTech vaccine, compared to 728,321 matched controls who received only two doses of the same vaccine for at least five months before.
Among the study participants, the majority have an average age of 50 years and 51% are women.
Vaccine efficacy was considered similar for different genders, age groups (ages 40 to 69 years and 70 years or older) and number of comorbidities.
The study was conducted between July 30 and September 23, 2021. The Delta variant was dominant in Israel during this period.
The Clalit Research Institute, in collaboration with researchers at Harvard University, analyzed one of the largest integrated databases of health records to examine the efficacy of the third dose of Pfizer / BioNTech vaccine against the Delta variant of SARS-CoV-2.
“These results convincingly show that the third dose of the vaccine is highly effective against serious Covid-19-related outcomes in different age groups and population subgroups one week after the third dose. This data should facilitate informed policy decision-making,” said Ran Balicer of the Clalit Research Institute, who also serves as chairman of Israel’s National Expert Advisory Team in response to Covid-19.
Ben Reis, director of the Predictive Medicine Group of the Computer Health Informatics Program at Boston Children’s Hospital and Harvard Medical School, said the study results should bolster information about the vaccine’s effectiveness.
“This careful epidemiological study provides reliable information about the effectiveness of the third dose of the vaccine, which we hope will be useful for those who have not yet decided to give the third dose.”
The study was conducted in Israel, as the country is one of the first global leaders in third-dose Covid-19 vaccination rates.
According to the researchers, the study provides the largest peer-reviewed assessment of the effectiveness of a “booster” dose of a Covid-19 vaccine in a mass vaccination setting.
Need for the third dose
Many countries are experiencing a resurgence of SARS-CoV-2 infections, despite vaccination campaigns so far being successful. This may be due to the increased infectivity of the delta variant and the decreased immunity of vaccines given months earlier.
In light of the current resurgence, several countries are planning to administer a third booster dose of the Covid-19 mRNA vaccine.
And given this need, the study also allows for a more accurate assessment of the effectiveness of the third vaccine at different periods, different subpopulations (by sex, age and number of comorbidities) and different results, the researchers point out.
Reference: CNN Brasil
