Photo/Illutration A health care worker prepares to administer a shot of Moderna vaccine at a medical institution in Chiba on June 21. (Asahi Shimbun file photo)

The health ministry is preparing to recommend males in their teens and 20s get the Pfizer COVID-19 vaccine instead of Moderna over concerns the latter could cause heart muscle inflammation, sources said.

The ministry is simply trying to play it safe with the vaccine rollout by issuing the recommendation, the sources said. It comes after reports emerged from overseas of rare incidences where young men developed inflamed heart muscles.

Officials at the Ministry of Health, Labor and Welfare are set to discuss the planned guidance at a meeting with a COVID-19 expert panel on Oct. 15.

Countries in Northern Europe have made similar moves to opt young people out of getting Moderna jabs.

Sweden has suspended its use for people aged 30 or younger.

In Denmark, people 17 or younger are temporarily ineligible to receive the Moderna vaccine.

The countries cite the possibility of developing side effects such as myocarditis, which is heart muscle inflammation, and pericarditis, which is inflammation of the outer lining of the heart.

Data as of Sept. 12 in Japan showed that 21.6 teenage males and 17.06 males in their 20s per 1 million males developed myocarditis or pericarditis after they received the Moderna vaccine.

In Japan, there were relatively fewer young people who got the Pfizer vaccine compared with their peers who were given the Moderna shot.

But according to some reports, the comparable numbers came to 1.87 teenage males and 13.08 males in their 20s per 1 million for those who were provided the Pfizer vaccine.

The reports said that even if recipients developed myocarditis or pericarditis, most cases were mild.

The ministry is also leaning toward recommending that those who got the Moderna vaccine for their first shot switch to the Pfizer vaccine for their second.