Japan's health ministry has decided to roll out a third dose of the coronavirus vaccine, with details such as the starting date and targets to be determined later.
An expert panel endorsed the ministry's plan for the booster shot on Friday.
People who have received two doses of Pfizer, Moderna or AstraZeneca vaccine are to get another from the same maker in principle.
Ministry officials proposed targeting people who received their second dose at least eight months ago. But panel members said the idea lacks scientific grounds, and called for further studies.
Officials also decided to monitor progress abroad before judging whether the boosters should be given to all inoculated people or only those at high risk of developing severe COVID-19.
Studies have shown that vaccine efficacy wanes over time. Panel members were split on how quickly the additional dose should be administered.
Some called for an early start, citing a rise in breakthrough infections among medical workers. Others said completing the two-dose regimen is a higher priority. They agreed to continue discussions.
Countries including Israel and France have already started giving third shots. The United States plans to kick off its booster program this month.