A booster shot of the Pfizer-BioNTech COVID-19 vaccine is effective against the Delta variant, according to an Israeli study of nearly 4.7 million adults.
The study found that people who had the Pfizer booster shot are 10 times less likely to become infected and nearly 18 times less likely to get a severe infection.
Growing evidence shows that the efficacy of the COVID-19 vaccine begins to wane after six months. In response, in mid-2021 Israel became the first country in the world to officially launch a third “booster” dose program, as part of one of the fastest and most comprehensive vaccine rollouts worldwide. This has been a boon for science, providing real-world data outside of clinical trials.
This new study, which appears in the New England Journal of Medicine, looked at medical data from 4,621,836 individuals over 16 years of age from 30 July to 10 October 2021. It found a tenfold lower COVID-19 infection rate in those who had received a booster at least 5 months after their first two doses, compared to those who had received two doses of a vaccine but hadn’t yet received a booster. This was the observed pattern across all age groups.
It also found that severe illness was less likely in those who had received a booster in the 40-60 and over-80 age groups.
A second study, in the same journal, looked at more than 840,000 individuals to find that participants over 50 who had received a booster shot had 90% lower mortality from COVID-19 than those who had not had a booster.
According to Dr Roger Lord, a medical scientist from the Australian Catholic University who was not involved in the study, this finding is “impressive”.
“The finding certainly lends strong evidence to the value of a booster vaccination at approximately 6 months following vaccination with the Pfizer COVID-19 vaccine,” he says. But he adds that these two studies do not compare the booster shot to the alternative of natural exposure – that is, the potential for a COVID-19 infection itself to generate an immune response in an individual during the same time period.
These studies also build on previous analysis from the same team showing the effectiveness of booster shots on people over 60, now looking at younger age groups with participants 16 years and older.
“Understanding the protective effect of the booster dose in younger age groups is key for forming public health policy,” explain the authors of the first paper, led by Yinon M. Bar-On from the Weizmann Institute of Science in Israel.
“Booster vaccination programs may provide a way to control transmission without costly social-distancing measures and quarantines.”
This new research also follows the results released last week of the phase 2 clinical trial of booster shots in the UK. The trial looked at the safety, immune response and side-effects of a third dose of seven different COVID-19 vaccines including Pfizer, and found them to be safe and effective.
Australia is now offering booster shots of Pfizer to anyone over the age of 18 who received their second dose of a COVID-19 vaccination at least six months ago.
“The arrival of the Omicron variant of COVID-19 and other variants that will follow also raises the question of how often boosters will be needed and how effective will this approach be as new variants arise,” Lord says. “COVID-19 has the greatest propensity to mutate in countries where vaccination rates are low so unless this is addressed we may be caught in a cycle of booster vaccination to deal with new variants as they arise.”
Lauren Fuge is a science journalist at Cosmos. She holds a BSc in physics from the University of Adelaide and a BA in English and creative writing from Flinders University.
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