Israeli researchers have determined that a third (“booster”) dose of the Pfizer-BioNTech vaccine is effective at preventing both infection and severe illness, according to a first-in-world study published September 15 in The New England Journal of Medicine.
Findings suggest that the third dose boosts immunity about tenfold compared to those who had received only two doses of the vaccine at least five months earlier.
The study was done by an interdisciplinary group of experts from the Weizmann Institute of Science, Ministry of Health, Technion–Israel Institute of Technology, Hebrew University of Jerusalem, Gertner Institute at Sheba Medical Center and the KI Research Institute.
Israel offers a unique perspective, as it was the first country in the world to vaccinate a significant portion of its population, and the first to endorse a formal booster vaccination policy.
By the end of March 2021, more than half of Israel’s population was vaccinated with two doses of the Pfizer-BioNTech vaccine – many weeks before most countries.
Encouraging results were quick to follow: Covid-19 incidence dropped from about 900 cases per million per day in mid-January 2021 to fewer than two cases per million per day by June 2021.
Delta effects
Nevertheless, Israel has been facing a widespread infection resurgence. By the end of August, infection rates reached over 10,000 confirmed daily cases and more than 600 people were hospitalized with severe illness.
Experts believe the spike happened for two reasons: the rise of the so-called Delta variant – a more transmissible variant of SARS-CoV-2 – and the waning of the Pfizer vaccine’s effectiveness over time.
In response, Israeli authorities approved the administration of a booster dose in mid-July, first to high-risk populations, and by the end of July to anyone aged 60 and older. Soon after, the booster campaign was expanded to include all vaccinated Israelis who had received their second dose at least five months earlier.
As of now, nearly three million citizens have received a booster dose.
Study of a million Israelis
The researchers examined data on more than a million Israeli adults, half who had not received the third shot and half who did.
Twelve days or more after the booster dose was administered, the rate of confirmed infections and of severe illness cases was more than 10 times lower in the booster cohort compared to the non-booster cohort.
An additional analysis, aimed at neutralizing possible behavioral differences between the two cohorts, revealed that the booster cohort had about a five-fold lower rate of confirmed infections.
Overall, 4,439 new confirmed cases of Covid-19 and 294 cases of severe illness were reported in the non-booster cohort, compared to 934 new cases and 29 severely ill individuals in the booster cohort.
Other studies have shown that individuals vaccinated six months earlier with two doses have approximately half the risk of contracting the Delta variant compared to unvaccinated individuals. According to the Israeli study, the booster dose reduces the susceptibility to confirmed infection to approximately 5 percent.
Furthermore, Health Ministry statistics show no serious cases in people 60 and over who got infected after having the booster shot.
About 7,400 new Covid cases were confirmed on September 18, and the weekly average number of infections fell from 9,416 during the week of August 29 to September 4, to 7,529 the week of September 12.
In the United States, advisers to the US Food and Drug Administration voted unanimously on Friday to recommend that the agency authorize a booster shot of the Pfizer-BioNTech coronavirus vaccine six months after vaccination only for people 65 years and older and for anyone at risk for severe illness, not to the broad public.
Epidemiologist Dr. Ran Balicer, founding director of Clalit Research Institute, explained the policy discrepancy in a tweet. He wrote that the United States felt a lower sense of urgency because its population was vaccinated later than Israel’s; is waiting on proper studies (likely from Israel) on safety and efficacy of the third dose; and prefers to act gradually, in contrast to Israel.
However, the researchers found that the risk of myocarditis and of many other serious adverse events was substantially increased after SARS-CoV-2 infection – suggesting it’s safer to get the vaccine than the disease.
