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Scientists report new risk from Pfizer vaccine

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A new study, published in the scientific journal New England Journal of Medicine, found that the Pfizer coronavirus vaccine slightly increases the likelihood of heart disease, in particular, myocarditis.

Vaccination was linked to an increased risk of myocarditis (risk ratio [RR] 3.24, 95 percent CI 1.55-12.44, risk difference 2.7 events per 100,000 people), as well as lymphadenopathy (RR 2.43, 95 percent CI 2.05-2.78, 78.4 per 100,000), appendicitis (RR 1.40, 95 percent CI 1.02-2.01, 5.0 per 100,000), and herpes zoster infection (RR 1.43, 95 percent).

But, in another cohort, published in the New England Journal of Medicine, SARS-CoV-2 infection was associated with a higher risk of myocarditis (RR 18.28, 95% CI 3.95-25.12, 11.0 per 100,000), as well as other cardiovascular complications, including acute kidney injury (RR 14.83, 95% CI 9.24-28.75, 125.4 per 100,000), pulmonary embolism (RR 12.14, 95% CI 6.89-29.20, 61.7 per 100,000), and intracranial hemorrhage (RR 6.89, 95% CI 1.90-19.16, 7.6 per 100,000).

They said that vaccination was “substantially protective” against anemia, acute kidney injury, intracranial hemorrhage, and lymphopenia.

Balicer’s team studied data from Israel’s largest healthcare institution to evaluate the occurrence of adverse events among vaccinated vs unvaccinated people, and they assessed the effects of SARS-CoV-2 infection on these adverse events.

Participants in the vaccine cohorts were 16 and older, had been in the health organisation for a full year, had no prior COVID-19 infection, and had had no contact with the healthcare system in the previous 7 days. Notably, populations with confounders such as healthcare employees, long-term care facility residents, or persons restricted to their homes for medical reasons, were excluded.

While it may be tempting to compare the risks of vaccination with infection, the authors warn against this.

“The effects of vaccination and of SARS-CoV-2 infection were estimated with different cohorts,” they wrote.

“Thus, they should be treated as separate sets of results rather than directly compared.”

From December 20, 2020 to May 24, 2021, eligible people who were vaccinated on a specific day were matched to eligible unvaccinated controls based on age, gender, place of residence, socioeconomic position, and population sector. The trial comprised a 21-day follow-up period after the first and second Pfizer vaccine doses. Patients were tracked for each adverse event from the day of matching until documentation of the adverse event, 42 days, the end of the research term, or death.

To “place the magnitude of the adverse effects of the vaccine in context,” Balicer and team also estimated the effects of SARS-CoV-2 infection on these same adverse effects during the 42 days after diagnosis.

Overall, 884,828 people each were included in the vaccination cohort and the unvaccinated cohort, though 235,541 in the unvaccinated cohort had to be rematched following vaccination. The researchers also included 173,106 people with COVID-19 infection matched with the same number of uninfected people.

The median age of the eligible cohort of 1,736,832 people was 43, and 48% were women. Median age in the vaccination cohorts was 38. Median age of the infection cohort was 36, and 54% were women.

Limitations to the study included that study participants were not randomly assigned according to exposures, which could introduce confounding and bias, and that the matching process resulted in a study population whose median age was 5 years younger than the eligible population. In addition, certain high-risk populations were excluded from the study.

The researchers compared the likelihood of developing a particular disease in vaccinated and unvaccinated people who had not previously been diagnosed with the disease. The same study was carried out among those who had been ill and did not recover from COVID-19.

“This study found that the BNT162b2 vaccine was not associated with an increased risk of most of the side effects studied in a nationwide mass vaccination setting. The vaccine is associated with a high likelihood of myocarditis (one to five cases per 100,000 people),” the study authors said.

According to scientists, the risk of this potentially serious disease is significantly higher in those infected with coronavirus – 11 cases per 100 thousand people.

In addition, the vaccine slightly increases the likelihood of appendicitis, herpes zoster, pericarditis, arrhythmias, myocardial infarction and other dangerous diseases.

Image Credit: Hannah Beier/Bloomberg via Getty Images

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