Japan is to begin administering coronavirus vaccines that target Omicron on Tuesday to people aged 12 or older who have received their first two shots.
Those eligible must be at least five months away from their most recent shot.
Elderly people and healthcare workers who have yet to get their fourth doses will be among the first in line for the Omicron-targeting booster. Local municipalities are expected to gradually expand the scope of those eligible for the jab at their discretion by mid-October.
Tokyo's Minato Ward is set to launch its booster campaign on Tuesday. Other municipalities are preparing to start theirs as soon as possible.
Under the current rules, every eligible person can get one shot only.
The health ministry has asked local authorities to accept holders of unused vaccination vouchers as eligible for the booster, and to send new vouchers to those who don't have any by the end of October.
Health ministry officials expect the Pfizer and Moderna vaccines being rolled out in the latest efforts to be more effective against Omicron variants than previous jabs. The officials say these vaccines are highly likely to work against future variants as well.
The ministry aims to complete the vaccination of people who want to receive one by year-end, as it braces for the anticipated next wave of infection around that time. It is also planning to shorten the five-month period between the Omicron-targeting booster and the previous dose.
The large-scale vaccination centers run by the Self-Defense Forces in Tokyo and Osaka will administer the Moderna jab starting on October 3 for people who have received their third shots. The daily quota for inoculations will be 1,000 people in Tokyo, and 500 in Osaka.