The COVID-19 subcommittee of the WHO Global Advisory Committee on Vaccine Safety (GACVS) is reviewing reports of a small number of cases of myocarditis reported in individuals vaccinated with the COVID-19 mRNA vaccines. The subcommittee noted that in most of the reported cases, the individuals have recovered. The subcommittee is soliciting and monitoring for additional information to assess for any relationship to COVID-19 vaccination.
Myocarditis is an inflammation of the heart muscle and pericarditis is an inflammation of the lining that surrounds the heart. While it can cause serious illness, it is frequently mild and responds well to conservative treatment.
On May 17, the US Advisory Committee on Immunization Practices (ACIP) COVID-19 Vaccine Safety Technical (VaST) Work Group concluded that there are few reports of myocarditis to date and that these cases seem to occur predominantly in adolescents and young adults, more often in males than females, more often after the second dose of the vaccine, and typically within 4 days after vaccination . Most cases appeared to be mild and follow up is ongoing.
The GACVS subcommittee noted that most of the information received so far is based on spontaneous, passive reporting. More rigorous studies using alternative data sources and more robust study designs including comparison of vaccinated and unvaccinated populations are needed to assess a potential causal association between the event and the vaccine. Some countries, such as Israel, the United Kingdom and the United States have embarked upon such studies. The GACVS subcommittee will review further as more data become available. The subcommittee also underscored the importance of having a harmonized case definition. A draft case definition for myocarditis has been developed recently by the Brighton Collaboration .
While acknowledging the clear benefits of the mRNA vaccines in reducing deaths and hospitalizations due to COVID-19 infections, the subcommittee encourages all health professionals to report all events of myocarditis and other adverse events observed with these and other vaccines. The WHO COVID-19 vaccine safety surveillance manual provides guidance to countries on the safety monitoring and adverse events data sharing for the new COVID-19 vaccines .
The GACVS COVID-19 subcommittee will continue to review the safety data from all COVID-19 vaccines and update any advice as necessary. Open, transparent, and evidence-based communication about the potential benefits and risks to recipients and the community is essential to maintain trust. WHO is carefully monitoring the rollout of all COVID-19 vaccines and will continue to work closely with countries to manage potential risks, and to use science and data to drive response and recommendations.