2nd COVID Booster Deemed 'Safe' by Israeli PM, But Some Experts Aren't So Sure

COVID-19 Second Booster Fourth Dose Israel Safety
Israeli Prime Minister Naftali Bennett said early data indicated a second COVID-19 booster dose was "safe" and effective. Above, a medical worker prepares a vaccine dose in Tel Aviv, Israel, on Jan. 3, 2022. JACK GUEZ/AFP/Getty

Israeli Prime Minister Naftali Bennett has deemed a fourth dose of Pfizer/BioNTech's COVID-19 vaccine "safe" and effective, while some experts are urging the public to wait for a final verdict.

Bennett cited what he said were the preliminary results of an Israeli study as he touted a "higher degree of certainty" for the safety of the second booster shots while speaking to the press at Sheba Medical Center on Tuesday, according to Reuters. He also said that the data was showing the shots resulted in a five-fold increase in antibodies, possibly bolstering protection from infection and reducing the severity of illness in those who get breakthrough infections.

"A week into the fourth dose, we know to a higher degree of certainty that the fourth dose is safe," Bennett said on Tuesday. "The second piece of news: We know that a week after administration of a fourth dose, we see a five-fold increase in the number of antibodies in the vaccinated person."

"This most likely means a significant increase against infection and ... hospitalization and (severe) symptoms," added Bennett.

Israeli health authorities recommended the fourth vaccine dose for people over 60 and healthcare workers last month amid a global surge of infections fueled by the highly contagious Omicron variant. No similar recommendations have been made by the U.S. Centers for Disease Control and Prevention (CDC), while the World Health Organization has not yet endorsed an initial booster, citing an inequitable distribution of vaccine doses around the world.

Regardless, immunocompromised people in the U.S. are increasingly seeking their own unapproved second booster doses out of desperation, according to The New York Times. The practice has been discouraged by medical experts who are warning that additional research is needed. Research has already shown that an initial booster dose is safe and generally increases vaccine effectiveness against Omicron.

"This is, at this point, probably more improv than science," Robert Wachter, chair of the department of medicine for the University of California at San Francisco, told the Times regarding the pre-emptive rush for second boosters.

Safety concerns about the fourth dose are mostly centered on exposing people to unnecessary risks that already come with vaccine doses. Side effects in the new Israeli study were similar to those seen previously, with the most common complaints being pain at the injection site, fever and headaches.

Experts say that concerns about additional boosters causing "fatigue" to the immune system are largely unwarranted. However, the timing of the shots could be critical, with boosters given too early possibly being less effective than those given later.

"There's really no reason why the immune system would become fatigued or not be able to respond," Dr. Cynthia Gay, an infectious disease professor at the University of North Carolina Chapel Hill School of Medicine, told WNCN. "You probably don't get the same bang for the buck with giving a booster too early, for example, or giving one when it's not needed."

There is also a chance that a fourth vaccine dose might not make any difference for immunocompromised people whose immune systems have failed to adequately respond to their first three doses.

In addition to the ongoing Israeli study testing fourth doses, a Sheba Medical Center trial beginning this week will test suggestions that mixing-and-matching vaccines improves effectiveness by giving recipients of three Pfizer doses a booster of Moderna vaccine.

Although second booster doses have not yet been approved in the U.S., immunocompromised people could still legitimately get a fourth dose as early as late February due to CDC guidance allowing for members of the eligible group to get additional doses six months after their third dose.

Newsweek reached out to the CDC for comment.