Inflammation risk highest among 16-24 age group after 2nd vaccine dose

A connection exists between mRNA coronavirus nations and cases of myocarditis that occur after them, according to a recent study conducted by the Finnish Institute for Health and Welfare (THL) in cooperation with the Nordic Countries.

The discovery is in line with results from previous monitoring, said the THL in a press release on Wednesday referring to the study.

The study followed up the risk of an inflammation of the heart muscle, myocarditis, requiring hospitalisationwithin four weeks of receiving coronavirus vaccination.

The study examined 23 million people living in Finland, Sweden, Norway, or Denmark.

The results show that the risk of inflammation is highest among young men aged 16-24 after the second vaccine dose.

Compared with the unvaccinated population, their risk of developing an extra case of myocarditis within 28 days of a second vaccination is as follows:

With Moderna's Spikevax 9-28 persons out of 100,000 will be affected.

With Biontech-Pfizer's Comirnanty vaccine 4–7 persons out of 100,000 will be affected.

Myocarditis is less prevalent among people other than men aged 16-24.

In the 28 days that follow a second vaccination the onset of myocarditis is as follows: of all men and boys 12 years and older, 4-6 out of 100,000 recipients of the Spikevax vaccine and fewer than one recipient out of 100,000 who were given the Comirnaty vaccine develop myocarditis.

Among girls and women 12 years old and above, the corresponding number for Spikevax is fewer than one, while for Comirnaty, there was no difference compared with the unvaccinated population.

“Although the study confirms that those taking the vaccine have a higher risk of myocarditis, the cases are very rare. Most are mild and probably of short duration. Only 40 percent of those ending up hospitalised need to spend more than 3 days in hospital”, said Petteri Hovi, Senior Researcher at THL.

Cases of myocarditis are more prevalent especially in young men also after a coronavirus infection or other infections, such as seasonal influenza.

“The results of the research need to be examined in relation to the benefits of coronavirus vaccinations. The vaccine protects against very serious coronavirus symptoms, and it is still worth taking. Since October 2021 men and boys under the age of 30 have been recommended the Spikevax vaccine instead of the Cominarty vaccine”, Hovi said.

The results of the study have affected the current product descriptions of the vaccines.

The results will also be used in the future in the further development of the vaccines, and in decision-making on vaccinations both in Finland and internationally.

Finland has also gradually amassed results from research on myocarditis after third vaccinations among men aged 16-39 and among all persons aged 12 and over.

After third doses, the target groups that were studied were not shown to have a higher risk of myocarditis compared with the unvaccinated population.