Israeli data provides ‘safety assurances’ to world on fourth COVID shots — study

As winter sets in and health workers in many countries meet hesitance regarding 2nd booster, major Israeli research explores safety and concludes there’s no cause for concern

Nathan Jeffay is The Times of Israel's health and science correspondent

An Israeli woman receives her fourth dose of the coronavirus vaccine in a private nursing home in Petah Tikva, on Tuesday, Jan. 4, 2022.  (AP Photo/Ariel Schalit)
An Israeli woman receives her fourth dose of the coronavirus vaccine in a private nursing home in Petah Tikva, on Tuesday, Jan. 4, 2022. (AP Photo/Ariel Schalit)

Israeli data provides “safety assurances to the global population” regarding fourth COVID-19 shots, according to a new peer-reviewed study.

As winter gets underway in the northern hemisphere and COVID cases are expected to spike, health workers in many countries are facing an uphill struggle to get people to take boosters of the coronavirus vaccine.

First, second and third shots were widely accepted, being viewed as part of the initial regiment of vaccines.

But as people became eligible for fourth shots (and fifth doses for some in various countries, including Israel), there has been more resistance. Safety credentials are more widely questioned now that many view vaccines as less urgent than they initially were.

In Israel, while 6.1 million people took a second shot, only 900,000 have accepted a fourth shot.

A new study, published in The Lancet Respiratory Medicine, presents the first large-scale research into the safety of taking a fourth shot of the Pfizer vaccine.

“We believe this study provides safety assurances to the global population who are eligible to receive an additional COVID-19 booster inoculation,” wrote Prof. Dan Yamin from Tel Aviv University’s Center for Combating Pandemics, together with his co-authors.

“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.”

Yamin worked together with doctors and analysts from Maccabi Healthcare Services, which provided data from its patients in order to explore the safety of fourth shots. The study focused on regular Pfizer shots, which are still in widespread use, as opposed to those which were recently adapted to be more effective against more recent variants.

An Israeli medical worker prepares a coronavirus vaccine (Olivier Fitoussi/Flash90)

The study had two parts. The first involved analyzing anonymized medical records of 17,814 patients who took a fourth shot to detect side effects or “adverse events.” The authors wrote: “Comparing the 42 days before and after vaccination, the second booster was not associated with any of the 25 adverse events investigated.”

Despite the resounding conclusion from this data, there is always a possibility that patients are suffering from side effects that they aren’t reporting. That is why researchers recruited a cohort of Maccabi patients who agreed to wear smartwatches that monitored their health and granted access to their medical records.

The smartwatches monitored several physiological measures, including heart rate. A mobile app asked the patients daily to complete a self-reported questionnaire on their health. There were 699 patients who received fourth shots in this part of the study. For the sake of comparison, there were also patients who received a third shot during the time that data was collected.

The researchers found there was no notable difference in reactions to the fourth vaccine, which is seen by many as an unknown quantity, compared to the more familiar and widely accepted third shot. “We found no significant differences after inoculation with the first booster compared with the second booster,” they reported.

Fourth shots did elevate average heart rates beyond the baseline — meaning the pre-vaccination rate. They stayed high during the first three days following the second booster, peaking on day two. But mean heart rate values returned to baseline levels by day six, which is seen as a reasonable return to normal.

Dr. Dan Yamin of Tel Aviv University (Moshe Baderashi)

Yamin and his colleagues believe that their study can increase confidence in fourth shots and help overcome a major hurdle to their widespread adoption. They wrote: “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.

“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. 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.”

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