Risk of myocarditis very minor from COVID vaccine, Israeli research shows

The Clalit-Beilinson study analyzed medical information from 2.5 million members of the healthcare provider who vaccinated with Pfizer. 

Vials with Pfizer-BioNTech and Moderna coronavirus disease (COVID-19) vaccine labels are seen in this illustration picture taken March 19, 2021.  (photo credit: REUTERS/DADO RUVIC/ILLUSTRATION/FILE PHOTO)
Vials with Pfizer-BioNTech and Moderna coronavirus disease (COVID-19) vaccine labels are seen in this illustration picture taken March 19, 2021.
(photo credit: REUTERS/DADO RUVIC/ILLUSTRATION/FILE PHOTO)

The risk of experiencing myocarditis after receiving a coronavirus Pfizer vaccine remains very minor, two major Israeli studies published in the prestigious New England Journal of Medicine on Wednesday have shown. According to one piece of research, the vaccine does slightly increase the risk compared to that of the general population.

Only 2.13 individuals over 100,000 suffered from myocarditis after inoculation – or 0.0000213% according to a paper by researchers at Clalit Health Services and Rabin Medical Center-Beilinson Campus in Petah Tikva. Most cases were mild.

Myocarditis is an inflammation of the heart muscle which can be caused by a viral infection but also appears as a reaction to a medication. The symptoms include pain in the chest, arrhythmias, and shortness of breath.

The condition can also be developed as a consequence of COVID-19 infections themselves.

According to research by the US Centers for Disease and Controls, based on data collected in December 2020-January 2021, patients with COVID-19 had nearly 16 times the risk for myocarditis compared with patients who did not have COVID-19, and risk varied by sex and age.

The Clalit-Beilinson study analyzed medical information from 2.5 million members of the healthcare provider who vaccinated with Pfizer. 

 Health worker prepares a Covid-19 vaccine at a temporary Clalit health care center in Jerusalem, October 3, 2021.  (credit: YONATAN SINDEL/FLASH90) Health worker prepares a Covid-19 vaccine at a temporary Clalit health care center in Jerusalem, October 3, 2021. (credit: YONATAN SINDEL/FLASH90)

Some 54 cases of myocarditis were recorded, 76% of which were classified as mild, 22% intermediate. One case presented severe symptoms.

Men were more likely to present the side effect than women (4.12 compared to 0.23 every 100,000 individuals). The group with the highest incidence was young men between 16-29, with 10.69 cases per 100,000 persons.

“This study is the first to reliably assess the incidence of myocarditis, the main side effect found to be associated with the corona vaccine,” said Dr. Guy Witberg, a cardiologist at Beilinson. “The findings of the study show that this is a relatively rare side effect even in the population group at highest risk (young men).”

“The findings also show that in the vast majority of cases it is a mild disease with a benign course that does not significantly affect cardiac function in the short term and is not expected to affect patients’ health in the long term,” he added. “This is particularly significant in light of the fact that myocarditis is a disease characterized by a very wide range of clinical manifestations.”

“It is also important to remember that in a previous study we also demonstrated the increased risk of developing myocarditis after infection with the coronavirus,” said Prof. Ran Balicer, Clalit’s chief of innovation.

A second study led by Prof. Dror Mevorach, a senior physician from Hadassah-University Medical Center, with the cooperation of physicians from several Israeli hospitals as well as Health Ministry experts, analyzed medical records from the ministry beginning December 20, 2020, when the country started its vaccination drive, until May 31.

By that point, some 5.1 million Israelis had been fully inoculated, with around 9.29 shots.

According to the records, 304 cases of myocarditis were registered. Some 21 cases eventually received a different diagnosis. Of the remaining 283, some 142 were recorded among inoculated people within 21 days after the first shot and 30 days after the second shot, 40 among vaccinated people but not in proximity to vaccination, and 101 among unvaccinated, 29 of whom diagnosed with COVID.

“Overall, we estimated that definite or probable cases of myocarditis occurred in the overall Israeli population at a rate of approximately 1 per 26,000 males and 1 per 218,000 females after the second vaccine dose, with the highest risk again among young male recipients,” the authors wrote.

They compared the results with those of the study by Clalit.

“That study showed a somewhat lower incidence of myocarditis, possibly because of the different methods that were used,” the paper reads.

“On the basis of data from an Israeli national database, the incidence of myocarditis after two doses of the BNT162b2 mRNA vaccine was low but higher than the incidence among unvaccinated persons,” Mevorach and his coauthors concluded.

On Thursday, The Jerusalem Post learned that individuals vaccinated with the Pfizer coronavirus vaccine may be asked to avoid strenuous exercise and other physical activity for one week after receiving each dose due to the cases of myocarditis.

In a slide deck prepared for the Health Ministry’s advisory committee for epidemic control and coronavirus vaccines, which the Post reviewed, some health officials in the Epidemiology Division of the Health Ministry are recommending that individuals “avoid strenuous activity for one week after their second dose of the mRNA COVID-19 vaccines.”

Casual walking, stretching, working while standing and housework would all be acceptable.

If accepted, the guidelines that are given to vaccinated people after getting the jab would be updated.

“We recommend that everyone, in particular adolescents and young men aged under 30 avoid strenuous activity, such as intense exercise, for one week after the first and second doses,” the slide deck said.

It defined high-intensity exercise as circuit training, vigorous forms of weight training, sprinting and swimming longer distances.

The officials said that high-functioning athletes concerned about losing their conditioning could consider “downgrading their level of exercise” to a low intensity.

A member of the vaccine panel told the Post that although the matter would be discussed at the next meeting, most committee members are currently opposed to it.