Israeli study supports safety of fourth COVID-19 shot

A major peer-reviewed Israeli study on the safety of taking a fourth shot of the Pfizer COVID-19 vaccine reports “safety assurances to the global population.”

The Israeli study on a fourth Pfizer shot, published in The Lancet Respiratory Medicine journal, was authored by Prof. Dan Yamin of Tel Aviv University’s Center for Combating Pandemics. Yamin and his co-authors issued what he called “assurances to the global population who are eligible to receive an additional COVID-19 booster inoculation.”

“These assurances can help increase the number of high-risk individuals who opt to receive this booster vaccine, and thereby prevent severe outcomes associated with COVID-19,” they wrote. 

Yamin examined patient data collected by the Maccabi Healthcare Services HMO, to explore the safety of a fourth Pfizer shot. The study included data on the effects of Pfizer’s regular shots, as well as recently developed vaccines adapted to be more effective against newer variants.

The first part of the study analyzed medical records of 17,814 anonymous patients who took a fourth shot in order to detect side effects or “adverse events.”

“Comparing the 42 days before and after vaccination, the second booster was not associated with any of the 25 adverse events investigated,” the study said.

In such studies, it is possible adverse effects are underreported. To account for this possibility, the researchers used a group of 699 patients who agreed to wear smartwatches to monitor their health and gave the researchers access to their medical records. 

The smartwatches monitored several physiological measurements, including heart rate. The patients then used their phones to fill out a daily questionnaire regarding their health. A control group that had received a third shot was included in the study.

The researchers found no significant differences after inoculation in the group that took the fourth shot, compared with those who had taken the third shot.  

The fourth shot did cause a rise in heart rates beyond the baseline – meaning the pre-vaccination rate – which stayed high for the first three days following the second booster – peaking on day two, but returning to normal by day six. This was seen as a reasonable response. 

Yamin and his colleagues believe their study can improve confidence in the fourth shot and help overcome any objections to its application. 

“Despite the second Pfizer-BioNTech booster dose showing effectiveness in preventing the severe outcomes of COVID-19 with a promising safety profile, there has been a notable global public reluctance to be vaccinated,” they wrote. “In the USA, two months after the CDC recommendation, only 21.5% of eligible individuals had followed the suggestion to receive the [fourth shot].” 

“Studies indicate that COVID-19 vaccine hesitancy is mainly motivated by safety concerns rather than efficacy considerations,” they wrote. “Raising confidence in the booster vaccines requires closing the knowledge gap on vaccine safety, a gap that has thus far been filled by non-scientific, somewhat speculative theories.”

This study comes as winter approaches and COVID-19 cases are expected to increase. It also meets a new atmosphere of vaccine hesitancy. While many Israelis took the first, second and even third shots, there is some resistance to taking a fourth shot (and a fifth, in some countries, including Israel).

In Israel, 4.5 million people took the initial “booster,” the third shot, but only 893,000 have taken the fourth Pfizer is the only pharmaceutical company that provides COVID-19 treatments to Israel’s citizens per an agreement between the company and the previous government under Benjamin Netanyahu in 2020. 

Overall, 6.7 million Israelis got their first injection while 6.1 received the full initial two-shot dose. Some Israelis have opted for the fifth shot, but that figure was unavailable.