SARS-CoV-2 infections have been resurgent in many areas of the world throughout 2021, driven primarily by the Delta variantTrusted Source.
Healthcare officials worry that the effectiveness of current vaccination is waning, not holding up against this new strain. In response, many governments want to administer booster dosesTrusted Source of COVID-19 vaccines.
The Israeli government deployed third doses of the Pfizer vaccine before and during the country’s fourth wave of the pandemic in the summer of 2021.
A team led by scientists from Harvard University and Israel’s Clalit Research Institute recently concluded that this extra inoculation could significantly reduce the risk of severe complications of COVID-19.
Their paper, which appears in The LancetTrusted Source, summarizes the largest peer-reviewed study of a COVID-19 booster dose to date. This investigation is also the first to gauge how well a third dose of the Pfizer vaccine works to prevent severe outcomes.
The team analyzed data from Clalit Health Services, Israel’s largest healthcare organization.
The scientists followed 728,321 individuals who received a third Pfizer COVID-19 vaccine between July 2020 and September 2021. These participants were matched with an equal number of people who only received two doses of the vaccine.
The authors explain: “In this study, we estimated effectiveness starting from day 7 after the third dose, which is similar to the period used to define full vaccination after the second dose. Our choice is supported by high concentrations of antibodies in individuals 7 days after administration of the third dose.”
Primary outcomes included hospital admission related to COVID-19, severe disease, and mortality, according to National Institutes of Health (NIH) criteria.
As part of their analysis, the researchers adjusted for possible confounding factors, including sociodemographic factors, existing health conditions, and behavioral factors.