Japan's health ministry has listed inflammation of the heart muscle and of the outer lining of the heart in younger males as possible serious side effects of the Moderna and Pfizer COVID vaccines.
It says that as of November 14, out of every one million males who had the Moderna vaccine, such side effects were reported in 81.79 males in their teens and 48.76 males in their 20s.
The figures were 15.66 and 13.32 respectively for those who had the Pfizer vaccine.
The ministry held a panel of expert on Saturday and proposed warning of the risk by printing "serious side effects" on the documents attached to the vaccines.
It will also require hospitals to report in detail incidents involving people who developed the symptoms within 28 days after being vaccinated, according to the law.
The plan was approved by the panel, and the ministry will notify municipalities.