Published: 9 June 2021

Safety Information


Patients should NOT decline vaccination subject to a monitoring communication. If you have any concerns with your vaccination, please contact your healthcare professional. A monitoring communication does not mean that the vaccine, medicine or medical device causes an adverse reaction.

M2 Logo Myocarditis – a potential adverse reaction to Comirnaty (Pfizer COVID-19 vaccine)


Monitoring finishes on 31 December 2021

Medsafe is investigating a potential risk of myocarditis following vaccination with Comirnaty. The aim of this communication is to encourage further reports to obtain more information on this potential safety concern.

Medsafe has received two reports of myocarditis (inflammation of the heart muscle) and two reports of myo-pericarditis (inflammation of the bag-like membrane around the heart as well as the heart muscle) following vaccination with Comirnaty. A small number of myocarditis cases have also been reported in some other countries, such as Israel and the United States. The myocarditis in these cases has generally been mild and not required treatment. There is currently no suggestion that these cases are due to the vaccine but Medsafe is collaborating with international medicine regulators on this issue.

Products affected
Additional information
Regulator actions

Products affected

Product name Sponsor
Comirnaty Pfizer BioNTech

Additional information

Comirnaty is an mRNA vaccine given to prevent coronavirus disease 2019 (COVID-19) in adults and adolescents who are 16 years of age and older.

Myocarditis is an inflammation of the heart muscle wall. There are many possible causes of myocarditis, the most common being viral infection. Over 100 people are discharged from hospital with a principle diagnosis of myocarditis in New Zealand every year. Symptoms may be non-specific, such as constant tiredness and weakness or cough, or specific to the heart, such as chest pain or palpitations (a sensation of rapid or irregular heartbeat).

Most reported cases of myocarditis after vaccination with Comirnaty appear to be mild and occur within a week after receiving the vaccine, and the person has recovered without treatment. Predominantly adolescents and young adults have been affected and more commonly males. No causal association with the vaccine has been concluded.

The benefits of the Comirnaty vaccine still outweigh the risks.

Information about Comirnaty, including known side effects, can be found in the consumer medicine information (CMI) and data sheet.

Regulator actions

This issue was discussed with Medsafe’s Independent Safety Monitoring Board (ISMB) on 27 May. The recommendation from ISMB was to highlight this potential adverse reaction to Comirnaty as a M2 Logo) Monitoring Communication.


Please report any case of myocarditis in patients who have been vaccinated with Comirnaty. Please include information on:

  • the time between vaccination and onset of myocarditis
  • if any treatment was required
  • if any other medicines are being taken
  • any relevant medical history
  • if it occurred after the first or second dose of Comirnaty

Consumers and healthcare professionals are encouraged to report suspected adverse reactions to medicines to the Centre for Adverse Reactions Monitoring (CARM).

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