The recent publications in the Journal of the American Medical Association (JAMA) on the development of acute myocarditis following mRNA COVID-19 vaccine are interesting but difficult to directly infer causality.

Coxsackie B virus has previously been implicated in the development of myocarditis and experimental autoimmune models of the disease involve non-specific stimulation of the immune system to induce the condition. 

In the publication by Kim HW et al, the four patients described that developed acute myocarditis had elevated white blood cell counts (WBC) on admission to hospital (two were abnormal). 

Testing for COVID-19 infection and other respiratory viruses indicated a negative response however the possibility of infection with other pathogens to account for elevated WBC was not determined. 

Did these very rare cases of acute myocarditis arise from the combination of an infection and non-specific immune stimulation provided by the vaccination process? 

The authors clearly establish the development of myocarditis in the four patients but later indicate that methods for testing for COVID-19 infection or other respiratory viruses were not foolproof and that the development of myocarditis with non-mRNA COVID-19 vaccines remains unknown. 

Collectively, the chances of developing acute myocarditis after receiving a COVID-19 mRNA vaccine is extremely rare and this adverse event may involve other factors such as an underlying infection to initiate the process.

The two studies describe a small number of people, mainly young males, with inflammation of the heart muscle, so-called myocarditis, in the setting of Pfizer/Moderna COVID-19 vaccination.

The two studies show an association of vaccination with myocarditis but they certainly do not imply causation.

The incidence of myocarditis in these studies is exceedingly rare amongst those who are vaccinated, and is infinitely outweighed by the striking benefits of COVID-19 vaccination in preventing cardio-respiratory failure and death, especially in those with pre-existing cardiovascular disease.

The complication of myocarditis is exceedingly rare in these two studies - 27 cases (23+4) amongst over 3 million vaccinated.

The studies should remind clinicians that all vaccines have rare complications, and in this case, cardiac symptoms such as chest pain or shortness of breath should be investigated if they occur post-vaccination.

Despite exceedingly rare potential complications, population-wide vaccination remains the key to overcome the COVID-19 pandemic.

Although reported myocarditis or pericarditis cases after COVID-19 mRNA vaccinations are above expected background rates of both these conditions; they are a rare occurrence. In particular, more cases have been reported in the young adult male subgroup. Acute chest pain in the first few days after mRNA vaccination should prompt people to seek medical review. 

Thankfully, the overwhelming majority of overseas reported cases thus far have been mild and have made a rapid recovery. Importantly, COVID-19 mRNA vaccines remain highly effective at preventing COVID-19 disease and these rare adverse events pale in comparison to the serious long term cardiac injury and morbidity that is caused by SARS-CoV-2 infection. 

Detecting safety signals such as myocarditis/pericarditis demonstrate that both Australian and international vaccine safety surveillance systems are robust and constantly adapting to the latest available data. The main safety challenge with a large population-wide rollout is detecting and responding to signals such as these which were not evident in a clinical trial. The TGA and state-based surveillance systems, such as SAEFVIC [Surveillance of Adverse Events Following Vaccination In the Community] in Victoria, are actively identifying and providing information for groups like ATAGI [Australian Technical Advisory Group on Immunisation] to come to clinical safety decisions.

Australians want to know that our rollout is underpinned by a robust safety vaccine system, and any previous and future changes to the rollout system should be viewed in this context.