Myocarditis in boys and young men can occur more often after the Spikevax vaccine from Moderna
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Myocarditis (inflammation of the heart muscle) is a rare side effect of mRNA vaccines. The side effect is observed especially in boys and young men and mainly after the second dose. Updated knowledge indicates that this occurs more often with the use of Moderna's vaccine Spikevax than BioNTech / Pfizer's vaccine Comirnaty. This seems to apply regardless of which mRNA vaccine was given as the first dose.
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- We therefore emphasise again our recommendation that young people under the age of 18 who are to be vaccinated are offered Comirnaty regardless of which mRNA vaccine they received as the first dose. Men under the age of 30 should also consider choosing Comirnaty when they are to be vaccinated, says Geir Bukholm, Deputy Director General at the Norwegian Institute of Public Health (NIPH).
Monitoring analyses of reported adverse reactions from the United States have suggested that myocarditis may be more frequent when using Moderna's vaccine as a second dose than the BioNTech / Pfizer vaccine, but the numbers have been small and therefore uncertain. New monitoring data from Ontario, Canada, substantiates that this observation is correct, and preliminary monitoring data from Norway, Sweden and other countries could indicate the same.
The most common cause of myocarditis is viral infections, and a seasonal variation is observed; where it occurs more often in late summer and autumn than at other times of the year. Myocarditis is most common in young men and boys. An increased incidence of myocarditis has been seen after the use of mRNA vaccines, and here too it is more common in young men and boys. Most people who have been affected by the rare side effect of myocarditis after vaccination have had relatively mild symptoms and the people have recovered quickly with ordinary treatment of the disease.
Background for advice
Norway is collaborating with the other Nordic countries on health registry analyses to detect and investigate rare side effects. The combined data from all the Nordic countries gives strength to the analyses. The Nordic registry study looking at the incidence of myocarditis and pericarditis has not been completed, and therefore has not yet been published and final conclusions cannot yet be drawn from this study. Norwegian monitoring data included in the Nordic registry study indicate an increased incidence after Moderna as the second dose. The Norwegian Institute of Public Health is therefore now issuing a reminder of the advice not to give Spikevax to those under 18 years of age, and clarifying that men under 30 years of age should consider choosing Comirnaty, as a precautionary measure. The same has been done in Sweden.
However, the side effect is rare and the absolute risk is still low. Both of the two mRNA vaccines used in the Norwegian coronavirus immunisation program are good and very effective, and provide a high degree of protection against severe COVID-19 infection. Spikevax from Moderna seems to provide somewhat better protection than Comirnaty from BioNTech / Pfizer against both mild and serious disease caused by the Delta variant.
- Those who are to be vaccinated in the future can in any case choose the type of vaccine they want, both as the first and second dose, Bukholm continues. It is important to emphasise that Spikevax from Moderna is as effective a vaccine against COVID-19 as Comirnaty, and both types of vaccine are still recommended for those over 30 years of age.
Strengthens the current recommendation for those under 18
NIPH has already recommended that Comirnaty should be used for everyone under the age of 18. Children and adolescents under the age of 18 have previously been recommended to be administered Comirnaty as there is greater experience with the use of this vaccine in the age group, in line with the principle of precaution. The knowledge that myocarditis can occur more often after using Spikevax than Comirnaty, also in somewhat older age groups, strengthens the previous assessment. NIPH therefore emphasises the recommendation that children and young people aged 12 to 17 should be offered Comirnaty and not Spikevax. Those under the age of 18 who have received the first dose of Spikevax should receive the second dose of Comirnaty. This applies to approximately 3,500 young people born in 2004 and 2005 who have received Spikevax (4 % of those vaccinated), the rest have received Comirnaty.
Myocarditis in adolescents in connection with coronavirus vaccination
Myocarditis is a rare side effect of mRNA vaccines in which inflammation of the heart muscle occurs, and has been observed after vaccination with both Comirnaty (BioNTech / Pfizer) and Spikevax (Moderna). The condition occurs more frequently in younger age groups, especially among boys and younger men. This is mainly seen after the second vaccine dose. Symptoms usually start within a week after vaccination. Myocarditis also occurs after coronavirus infection.
The incidence is uncertain, as different countries have different reporting systems. For Norway, it is estimated that between 5 and 10 cases of myocarditis may occur after coronavirus vaccination in the 2004 and 2005 cohorts. The prognosis for this condition is good, and Norwegian cardiologists have assisted NIPH in assessing myocarditis and believe that this side effect should not prevent Norwegian young people from being offered an mRNA vaccine. Currently, adolescents under 16 years of age are not recommended a second dose.