The health ministry is considering recommending that men under 30 receive Pfizer Inc.’s COVID-19 vaccine rather than the shot developed by Moderna Inc., following an increase in reports of a rare heart disease occurring in younger men after they received the latter vaccine.
The move comes after Sweden halted use of the Moderna shot last week for people born in and after 1991, citing a Nordic study that showed a higher risk of inflammation of the heart muscle, a condition called myocarditis, among young people given the shot. Finland has also paused use of the Moderna jab in men born in 1991 or later.
Concerns have been brewing over myocarditis and pericarditis, the inflammation of the tissue surrounding the heart. For those conditions, there had been 21.60 suspected cases reported per 1 million boys between 10 and 19 who received the Moderna shot by Sept. 12, according to health ministry data published Oct. 1, while the figure was 17.06 for men ages 20 to 29. For those groups who got the Pfizer vaccine, those numbers were 1.87 and 13.08 cases, respectively.
In contrast, women in the same age groups who received the Moderna vaccine saw less than 0.8 case of those conditions per 1 million.
The halt also comes as analysis of side effects in the U.S. has shown a similar rise in myocarditis incidents when Moderna is used.
But experts, worried that such data may lead to vaccine hesitancy, say that it still is important to get vaccinated, as U.S. Centers for Disease Control and Prevention data shows that the risk of getting such heart conditions is far higher for those infected with the coronavirus, and similar findings have been made in Japan as well.
An analysis of hospitalized COVID-19 patients in Japan by the National Center for Global Health and Medicine found 834 cases of myocarditis and related symptoms per 1 million men age 15 to 40, compared with no cases for women in the same age group.
“The risk of myocarditis is much lower in people who got the Moderna vaccine than in those experiencing a natural infection (with the virus), so there’s no reason to halt its use,” said Tetsuo Nakayama, a project professor at the Kitasato Institute for Life Sciences and director of the Japanese Society of Clinical Virology. “The experts may be divided in their opinions on whether to switch the shots for young men to the Pfizer vaccine.”
The ministry will hold an expert panel to discuss the issue Friday. Also on the agenda is whether to give Pfizer’s vaccine as a second dose to men under 30 who received the Moderna shot the first time round.
Both Pfizer and Moderna’s vaccines have been authorized for use in Japan for people age 12 and above. The two messenger RNA vaccines initially showed an extremely high efficacy of more than 90% in clinical trials, but studies have since indicated that Moderna’s vaccine fares better than Pfizer’s over the long term in terms of protection, as its efficacy does not fall as steeply in the months after inoculation.
If the panel decides to recommend the Pfizer shots for young men under 30, it would still be possible for them to get the Moderna shot at their own risk, albeit with some additional hurdles, Nakayama said.
Most symptoms of myocarditis are said to be minor, but the health ministry has not released data on how many of the reported cases were serious, Nakayama said, adding that such details should be made public.
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