Why three Nordic countries have suspended Moderna vaccine

On October 6, Sweden and Denmark, followed by Finland a day later, suspended the use of Moderna’s mRNA vaccine for younger age groups after reports pointed to an increase in the number of myocarditis and pericarditis cases. Why three Nordic countries have suspended Moderna vaccine.

On October 6, Sweden and Denmark suspended the use of Moderna’s mRNA vaccine for younger age groups after reports pointed to an increase in the number of myocarditis and pericarditis cases. Myocarditis causes inflammation of heart muscle which can limit the organ’s ability to pump blood and can cause changes in heartbeat rhythms, while pericarditis causes inflammation of the outer lining of the heart.

A day later, Finland followed suit and paused the use of the Moderna vaccine in people younger than 30 years. Both Finland Health institute and the Swedish Public Health Agency now recommend Pfizer’s mRNA vaccine for people younger than 30 years as there is greater experience with the vaccine in this age group. The Swedish Agency said its decision is valid till December 1 this year.

“A Nordic study involving Finland, Sweden, Norway and Denmark found that men under the age of 30 who received Moderna Spikevax had a slightly higher risk than others of developing myocarditis,” Mika Salminen, director of the Finnish Institute for Health and Welfare told Reuters.

The Swedish Public Health Agency said that the connection [of myocarditis and pericarditis] is “especially clear when it comes to Moderna vaccine Spikevax, especially after the second dose”. For an individual, the risk of being affected by myocarditis and pericarditis is very small.  

Meanwhile, the U.K., Hong Kong and Norway, have recommended administering only a single dose of the Pfizer vaccine for children ages 12 and older.

Risk from Moderna versus Pfizer vaccines

On why the Moderna vaccine has a relatively increased risk of myocarditis and pericarditis after the second dose compared with Pfizer, Immunologist Dr. Satyajit Rath, formerly with the Delhi-based National Institute of Immunology says in an email that since the serious adverse events are extremely rare it is not even absolutely certain that there is really an increase in this ‘risk’ of myocarditis with the Moderna vaccine over the Pfizer vaccine. “The two vaccines have not been used in the same populations, and there may well be differences in the people who have received one versus the other which could contribute to this so-called difference in risk (rather than the vaccine),” says Dr. Rath. “Some minor difference in the chemical composition of the two vaccines may have contributed to this so-called risk; even though they are both mRNA vaccines, they are not identical.” He also mentions the higher dosage of 100 microgram used in the Moderna vaccine compared with 30 microgram for Pfizer might be another possibility.

Protection from just one dose

“One dose provides good protection against a severe disease course, and the protection will probably be better among adolescents at this age than for older age groups,” says Camilla Stoltenberg, Director-General of the Norwegian Institute of Public Health in a release. “We consider that the offer of one dose provides the clearest benefit for the individual adolescent when the benefit is weighed against possible disadvantages of the vaccine. The second dose will be considered when there is more knowledge from other countries that have come further in the vaccination of this age group.”

Studies in Israel have shown that within six months there is a reduction in vaccine effectiveness in preventing infection after two doses of the Pfizer vaccine. Based on this data, Dr. Rath says there is no evidence to indicate how long a single dose of COVID vaccines will remain effective for. “I do not expect that duration to be dramatically different from the one in adults. But in the first place, that is simply a guess, and in the second place, we have no idea of such a duration with a single dose even in adults,” he says.

Breaking the transmission chain

Young adults, adolescents and young children rarely suffer from severe disease. However, they are likely to get infected and transmit the virus to others even while not suffering from COVID-19 disease. Vaccination of adolescents and young children can help in breaking the transmission chain. But should young adults, adolescents and young children, who are not at great risk of severe risk, be given two doses of even the Pfizer vaccine that has an extremely small risk of causing inflammation of the heart for the sake of breaking the transmission chain?

“The greatest transmission-limiting effect of the vaccines is achieved when two vaccine doses are given. The NIPH [Norwegian Institute of Public Health] has assessed that for this age group [12-15 years], which to a lesser extent than adults and older adolescents has contributed to transmission. The individual considerations of offering vaccination are more important than the benefit to society of limiting transmission,” the NIPH said in a release.

Males mostly at risk

Even earlier, evidence showed a tiny risk of myocarditis and pericarditis when young adults received the second dose of Pfizer and Moderna vaccines. The risk was overwhelmingly seen in males, and after the second dose. “It is hard to get any grip on why males are more affected, because we have no idea, even if it turns out to be a real and reliable association (between vaccine and illness), what the mechanism involved is,” says Dr. Rath. “We do know that, independent of COVID-19 disease or vaccines, myocarditis is somewhat more common in men than in women. But again, we have no clarity about why this is so.”

Extremely rare risk

Now, two studies published in The New England Journal of Medicine have reported based on field data that myocarditis is extremely rare and predominantly seen in males and is mild. The condition resolves on its own within a month.

The first NEJM study found that of the nearly 5.1 million people vaccinated with the Pfizer vaccine between December 20, 2020 and May 31, 2021 in Israel only 136 cases of myocarditis were reported. Of the 136 cases, 129 people (95%) had only mild myocarditis. The study found that the incidence of myocarditis after two doses of vaccination was highest among males. They found that myocarditis occurred in the population at a “rate of approximately 1 per 26,000 males and 1 per 2,18,000 females after the second vaccine dose, with the highest risk again among young male recipients”. 

The study also found that the “overall risk difference between the first and second doses was 1.76 per 100,000 persons with the largest difference among male recipients between the ages of 16 and 19 years”.

The second study published in NEJM carried out in Israel looked at the incidence of myocarditis after full vaccination with the Pfizer vaccine in a large health-care organisation. The study found 54 cases of myocarditis from 2.5 million vaccinated health-care organisation members aged 16 years and above. In all, 76% of cases of myocarditis were mild, and the highest incidence (10.69 cases per 1,00,000 persons) was reported in male patients between the ages of 16 and 29 years. 

Published in The Hindu on October 9, 2021