Japan's health ministry has given the green light to booster shots using the Pfizer vaccine.
A panel of experts approved the vaccine at a meeting on Wednesday.
The ministry says a clinical study overseas shows that people given a third dose of the vaccine showed levels of neutralizing antibodies that were 3.3 times the levels seen after their second shot.
The booster will be made available to health workers starting next month.
But the shots are likely to be limited to people aged 18 and over. Standard inoculations are available to people aged 12 and over.
The experts say they lack data at this stage about the effectiveness and safety of giving Pfizer boosters to people 17 and under. The health ministry says it will consider lowering the age threshold once Pfizer can furnish more data.
Kitasato University Professor Nakayama Tetsuo said, "I think booster shots play an important role in terms of preparing for another wave of infections. In particular, boosters should be given to vulnerable groups of people at high risk of developing severe COVID if they get infected."
Health authorities reported at least 205 new infections nationwide on Wednesday. Single deaths were reported in three prefectures.