NHK has learned that Japan's health ministry is arranging to allow coronavirus booster vaccine doses to be administered to people who received their second shots at least six months before.
Sources say the ministry is making such an arrangement while considering keeping an interval of roughly eight months or more as a standard for booster shots in line with the initial plan.
The sources say the ministry took into account overseas reports suggesting that the efficacy of vaccines started to decline six months after second shots.
The sources say the ministry plans to present the new proposal at its advisory panel of experts on Monday.
The ministry has been asking local governments to make preparations so that they can start giving booster doses to individuals who received their second shots at least eight months before.
Under the current plan, such vaccinations are due to start for medical workers next month, and for elderly and other citizens in January.
But the ministry's latest proposal is expected to force some local governments to put forward their schedules for booster shots as some elderly people reach the six-month threshold by the end of the year.
Some local governments told NHK that they will have difficulty adjusting their preparations, and securing sufficient numbers of venues and staff.
Concerns are also growing over whether the central government will be able to supply enough doses in time for the start of the new plan.
The ministry begins to deliver Pfizer-BioNTech booster doses to local governments, medical institutions and other entities nationwide on Monday.