Very rare cases of myocarditis and pericarditis (inflammation of the heart muscle/pericardium) have been reported following vaccination with the COVID-19 mRNA vaccines. Cases generally occur within 14 days of vaccination and more frequently after the second dose and in younger men. After evaluating all available data, it may be concluded that there is at least a probable causal link between the vaccines and myocarditis/pericarditis. Healthcare professionals should pay attention to the signs and symptoms of myocarditis and pericarditis and inform vaccinated people that they should seek immediate medical advice and assistance in the event of chest pains, shortness of breath or palpitations. Strong physical exertion should be avoided if such symptoms occur until the cause of the symptoms has been ascertained.

Some Scandinavian countries recently suspended vaccination with Spikevax, the COVID-19 vaccine from Moderna, for people under 30 (Sweden, Finland) and under 18 (Denmark) years of age. These measures were taken in response to the provisional results of a study performed in Scandinavia which identified an elevated risk of myocarditis in people in these age groups after vaccination with the Moderna vaccine.

There are also differences in the reporting rates of this adverse reaction for the two vaccines in the spontaneous reporting from Switzerland. By 3 November, 199 cases of myocarditis and/or pericarditis with a suspected link to vaccinations had been reported in Switzerland out of a total of more than 11 million vaccine doses administered. Of these, 35 were linked with Comirnaty and 157 with Spikevax; in 7 cases, the vaccine has not yet been identified. The large majority of cases involved males (n = 154, 77.4%) and the mean age was 38 years (median: 53, range: 14 to 88 years). The persons affected received medical treatment and most have now recovered.

When interpreting these data it should be borne in mind that about twice as many people have been vaccinated with the Moderna vaccine in Switzerland and that, for reasons relating to the methodology used, spontaneous reports are only suitable to a limited extent as a basis for direct comparisons between individual vaccines.

Final results from the aforementioned Scandinavian study are not yet available. Other data, e.g. from the FDA in the USA, do not confirm an elevated risk of myocarditis following administration of the Moderna vaccine. All national and international data indicate, however, that – even in groups at increased risk – myocarditis is a very rare side effect and that the incidence of myocarditis in connection with COVID-19 disease is higher. Swissmedic will carefully examine the results of the Scandinavian study and other available information on myocarditis to ascertain whether measures need to be taken and, after conferring with other international authorities, will inform the public promptly.

In addition to the two mRNA vaccines Comirnaty and Spikevax, the vector-based vaccine from Janssen has also recently been used in Switzerland (though in a limited number of persons). The side effects profile of this vaccine differs from that of the mRNA vaccines in certain respects. However, it is important to have information about any specific, very rare side effects of this vaccine, such as thrombocytopenia thrombosis syndrome, capillary leak syndrome or Guillain-Barré syndrome, so that appropriate diagnostic and therapeutic measures can be taken in good time in such cases. For details regarding this vaccine, please consult the current Swiss Information for healthcare professionals.

Medical professionals are requested to report any serious and previously unknown side effects to Swissmedic. In doing so, they can actively help to improve knowledge of the safety profile of a medicinal product or vaccine. To submit reports, please use our electronic reporting portal ElViS.