Israeli study finds 4th vaccine dose (2nd booster) gives only short-term increase in protection



A fourth dose of Pfizer's COVID-19 vaccine only provides a short-term boost in protection against the virus, according to a study that was released Tuesday.

As Pfizer and BioNTech seek emergency authorization from the U.S. Food and Drug administration to provide a second COVID-19 booster shot to senior citizens, researchers in Israel have found that a fourth shot of the company's vaccine only provides four to seven weeks of increased protection before its efficacy wanes.

The study examined data from the Israeli Ministry of Health database on more than 1.25 million people who were 60 years of age or older and received their fourth Pfizer dose between January and March. At the time, the Omicron variant was predominant in Israel.

Researchers found that people who got the second booster shot were half as likely to test positive for COVID-19 four weeks later than people who only took three doses.

But by the eighth week, both groups were equally likely to catch the coronavirus, meaning the boost from the fourth shot wore off.

Scientists said that protection against severe illness did not wane during the study period and they suggested further studies are needed to determine how long that protection lasts.

"The results presented here indicate that as compared with three vaccine doses given at least 4 months earlier, a fourth dose provides added short-term protection against confirmed infections and severe illness caused by the omicron variant," the study authors wrote.

"Overall, these analyses provided evidence for the effectiveness of a fourth vaccine dose against severe illness caused by the omicron variant, as compared with a third dose administered more than 4 months earlier. For confirmed infection, a fourth dose appeared to provide only short-term protection and a modest absolute benefit," the study concluded.

Last week, the FDA authorized a second dose of booster shots for every American over the age of 50. U.S. officials said that the additional booster dose may be necessary because of waning protection against serious outcomes from COVID-19 in older and immunocompromised individuals. President Joe Biden received his second booster shot on March 30.

Previous studies have suggested that the the first booster dose provides a significant increase in protection against the virus compared to no vaccination, one shot, or two shots.

According to the U.S. Centers for Disease Control and Prevention, about 49% of U.S. adults who have been fully vaccinated have also received the first booster shot. About 68% of adults age 65 and older have done so.

Israeli study finds fourth mRNA vaccine dose 'may only have marginal benefits' for young, healthy people



Israeli researchers have found that a fourth mRNA coronavirus vaccine dose is safe but only "somewhat efficacious" against preventing infection from the COVID-19 Omicron variant.

The study, published Wednesday in the New England Journal of Medicine, assessed the efficacy of a fourth dose of either the Pfizer or Moderna vaccines in healthy young health care workers at the Sheba Medical Center. Interim results showed that a fourth shot "is immunogenic, safe, and somewhat efficacious (primarily against symptomatic disease)."

"A comparison of the initial response to the fourth dose with the peak response to a third dose did not show substantial differences in humoral response or in levels of Omicron-specific neutralizing antibodies," the study authors concluded. They suggested that a fourth shot "may have only marginal benefits" when given to healthy young people.

The study did not asses the efficacy of a fourth dose among older and more vulnerable populations.

“Among the approximate 600 participants, 270 of whom received either a fourth dose of the Pfizer vaccine or Moderna vaccine, we found no differences, both in terms of IgG antibody levels and in terms of neutralizing antibody levels, which reached a level similar to that measured a month after the third dose was administered,” lead study author Prof. Gili Regev-Yochay told the Jerusalem Post.

She said that for both the Pfizer and Moderna vaccines, health care workers who received a fourth dose only had a slightly lower infection rate than those in the control group.

“However, it should be emphasized that the third dose is extremely important for anyone who has not yet contracted COVID-19, and the fourth dose is most likely important for populations with risk factors for which a fourth vaccine would protect from serious illness," Regev-Yochay said.

“This study is added to a series of studies led by Sheba with the aim of providing a scientific basis for managing a pandemic that has wreaked havoc around the globe,” she concluded.

“Thanks to the cohort at Sheba and the plethora of data we have accumulated since the beginning of the pandemic, we continue to lead international studies which shed light on the behavior of the virus and the effectiveness of vaccines and serve decision makers in determining health policy in Israel and around the world.”

Pfizer and BioNTech on Wednesday asked the U.S. Food and Drug Administration to grant an emergency use authorization for a fourth COVID-19 shot for adults age 65 and older who have already received a booster vaccine dose.

In a press release statement, the companies cited the Sheba Medical Center study, as well as additional data from Israel that showed evidence that an additional mRNA booster shot lowered rates of confirmed infections and severe illness.

"An analysis of Israeli Ministry of Health records was conducted for over 1.1 million adults 60 years of age and older who had no known history of SARS-CoV-2 infection and were eligible for an additional (fourth dose) booster. These data showed rates of confirmed infections were 2 times lower and rates of severe illness were 4 times lower among individuals who received an additional booster dose of the Pfizer-BioNTech COVID-19 Vaccine administered at least four months after an initial booster (third) dose compared to those who received only one booster dose," the release said.