Pfizer and Moderna vaccines: UK adds rare heart inflammation to side effects

The UK’s drugs regulator has added extremely rare occurrences of heart inflammation to the official list of side effects for the Pfizer and Moderna vaccines.

The Medicines and Healthcare products Regulatory Agency (MHRA) stressed that “the benefits of getting vaccinated outweigh the risks” and these “events are extremely rare and tend to be mild when they do occur”.

After conducting a review of 111 suspected reactions in the UK, the MHRA issued new advice for healthcare professionals and vaccine recipients.

It notes that there have been reports of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) after vaccination.

These cases were only for the Moderna and Pfizer vaccines and typically occurred in younger men within 10 days after their second dose.

Those vaccinated should also seek immediate medical attention if they experience new chest pain, shortness of breath, palpitations or abnormal heart rhythms.

Dr June Raine, MHRA chief executive said last week:

“We have carefully reviewed reports of suspected adverse reactions involving types of heart inflammation known as myocarditis and pericarditis.

“We have concluded that the Covid-19 vaccines made by Pfizer/BioNTech and Moderna may be linked with a small increase in the risk of these very rare conditions.

“The cases tended to be mild and the vast majority recovered with simple treatment and rest.”

The change of guidance follows similar action in the US, as the Centers for Disease Control and Prevention (CDC) noted the connection between the vaccines and heart inflammation last month.

CDC officials also acknowledged that symptoms were still “a rare event”. For both vaccines combined, there were 12.6 heart inflammation cases per million doses. The cases were more frequent among Moderna’s vaccine recipients at 19.8 cases per million versus eight cases per million for Pfizer’s.

Health officials and scientists are monitoring cases of the rare side effect in order to fully understand the potential risks, how to manage it, and whether it causes any long-term effects.

The MHRA added: “While reports of myocarditis and pericarditis after vaccination with COVID-19 vaccine AstraZeneca have also been received, there is insufficient evidence to recommend similar warnings for this vaccine.”

In April this year, the drugs regulator shrugged off concerns around heart inflammation. Following cases of the condition being reported in Israel, it said: “Based on our experience and safety monitoring in the UK, there is currently no new safety concerns raised regarding myocarditis.”