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Myocarditis Appears Rare After COVID-19 Vaccination

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Overall risk of development myocarditis A new report from British Columbia, Canada, shows that infection rates are low following COVID-19 vaccination.

However, due to certain risk factors, researchers recommended the Pfizer and Biontech vaccines be preferred over Moderna vaccines for patients aged 18 to 29.



Dr. Naveed Janjua

“Overall, myocarditis was low after SARS-CoV-2 vaccination, but especially high in young men after the second dose of Moderna mRNA vaccination. After the third dose, the incidence of myocarditis was low. said study author Naveed Janjua, MBBS, DrPH, Epidemiologist, executive director of data and analytics services at the British Columbia Center for Disease Control in Vancouver. Medscape Medical News.

“Although the observed incidence of myocarditis was higher than expected, the benefits of the vaccine in reducing COVID-19 severity, hospitalizations, and death far outweigh the risk of developing myocarditis.

the study published online November 21st Journal of the Canadian Medical Association.

British Columbia Cohort

Investigators analyzed administrative data from a COVID-19 cohort in British Columbia from December 2020 to March 2022. They focused on the mRNA-1273 vaccine, manufactured by Moderna, and the He BNT162b2 vaccine, manufactured by Pfizer-Biontech, and explained differences in age, gender and dosage. Number, type of vaccine.

The research team examined the incidence of hospitalization or emergency room visits for myocarditis or pericarditis within 7 to 21 days after vaccination, calculated as myocarditis rate per 100,000 mRNA vaccine doses. They also compared the observed number of cases to the calculated number of cases that would have been expected had there been no association between the vaccine and myocarditis. Data on emergency department visits were used to calculate expected rates, and 2019 rates were used for observed versus expected analyses.

Overall, British Columbia received more than 10.2 million doses of mRNA vaccine during the study period. This includes his nearly 7 million doses of Pfizer-BioNTech and his 3.2 million doses of Moderna. About 4 million were the first dose, about 3.9 million were his second dose, and 2.4 million were his third dose.

The researchers observed 99 cases of myocarditis within 7 days after vaccination, compared with the expected 7 cases. The incidence of myocarditis was 0.97 cases per 100,000 vaccine doses compared with an expected rate of 0.13 per 100,000 population. The observed to expected ratio was 14.81.

In addition, 141 cases were observed within 21 days after vaccination and the expected 20 cases were observed. The incidence of myocarditis was 1.37 cases per 100,000 vaccine doses compared with an expected rate of 0.39 per 100,000 population. The observed to expected ratio was 7.03.

In general, most myocardial inflammation cases were male and occurred after the second dose. Among patients with myocarditis, males were younger than females within 7 days of vaccination (28 vs. 45 years) and within 21 days of vaccination (31 vs. 49 years).

age and risk

When analyzed by age, the incidence of myocarditis was highest in patients aged 12-17 and 18-29 years and lowest in patients aged 70-79 years. The incidence of myocarditis was about 2.6 cases per 100,000 doses in people under 30 years of age.

By gender, the incidence of myocarditis was higher in men than in women. The incidence of myocarditis was 0.35 per 100,000 in women compared with 1.64 per 100,000 in men.

By number of doses, there were more cases of myocarditis among those who received the primary vaccine series. The incidence of myocarditis was approximately 2.5 per 100,000 for the first and his second dose, compared to 0.76 per 100,000 for the third dose.

By vaccine type, there were more cases of myocarditis among those who received the Moderna vaccine. 0.74 per 100,000 doses in Pfizer recipients.

Males aged 18-29 who received the Moderna vaccine had the highest ratio of observed versus expected after the second dose. The risk was nearly 3 per 100,000 cases compared to an overall expected rate of less than 1 per 100,000 cases.

Researchers also identified 179 cases of pericarditis within 7 days after vaccination and 308 cases within 21 days after vaccination. The incidence of pericarditis was 1.75 per 100,000 doses in the 7-day window, with an observed to expected ratio of 5.18, and 3 per 100,000 doses in the 21-day window, with an observed The ratio to the predictions made was 2.97.

Similar to the incidence of myocarditis, the incidence of pericarditis was higher in males, patients aged 12 to 29 years, Moderna recipients, and after the second vaccination.

Janjua noted that future studies need to monitor intermediate to long-term outcomes of myocarditis and the development of myocarditis, especially in children and young adults. Researchers are also interested in the risks after booster and updated vaccines, and potential causal links between mRNA vaccines and myocarditis.

low absolute number

C. Buddy Creech, MD, MPH told Medscape: Creech is Director of the Vanderbilt Vaccine Research Program and Professor of Pediatrics at the Vanderbilt University School of Medicine in Nashville, Tennessee.



Dr. C. Buddy Creech

Although not involved in this research, Creech has led clinical trials of a COVID-19 vaccine throughout the pandemic. Pfizer, Moderna, the Centers for Disease Control and Prevention, and the National Institutes of Health have launched large-scale studies to understand potential links between vaccines and myocarditis risk, he noted.

“Perhaps most importantly, cases of post-vaccination myocarditis are very mild and often do not require treatment. It should give some confidence to parents trying to protect their families from COVID disease, including.”

It is difficult to establish a causal link between vaccines, foods, or drugs and side effects, Creech said. Because certain things, called side effects, occur naturally.”

For example, Creech explains: diarrhea vomiting after eating at a restaurant, food poisoningHowever, they may have actually contracted the stomach virus by interacting with people in another public space. The emphasis has been on identifying causes and related factors.

“The key to this problem is that people, especially young men between the ages of 15 and 30, develop myocarditis after other viral infections such as the common cold,” Creech said. “Sometimes vaccines happen to be involved right before a diagnosis is made.”

This study was supported by the Canadian Immunization Research Network through grants from the Public Health Agency of Canada and the Canadian Institutes of Health Research, and funding from the Public Health Agency of Canada through the Vaccine Surveillance Reference Group and COVID-19. Immunity Task Force. Janjua reported honoraria from her AbbVie and Gilead outside of this study. Creech has not reported any related financial relationships.

CMAJ. Published online on November 21, 2022. full text

Carolyn Crist is a health and medical journalist reporting on the latest research for Medscape, MDedge and WebMD.

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