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Anyone in Japan aged 18 and older who wants a booster shot—and has already received two doses of the Pfizer, Moderna or AstraZeneca vaccines—is eligible. In particular, people at high risk of exposure and serious illness, such as medical workers, the elderly, and those with underlying diseases, are encouraged to get one.
Medical workers first
The health ministry has been offering boosters to medical workers since December 1. The next priority group will be people aged 65 and older followed by the rest of the population. Boosters will be administered at some workplaces and on university campuses from March. Official figures show that about 78 percent of the population has already received two doses.
Shorter intervals planned
The government initially set the minimum interval between receiving a second and third dose at eight months. A six-month interval applies to people related to medical institutions and elderly care facilities with cluster infections.
The shorter interval will apply to other people, including medical workers, long-term hospital patients and residents of elderly care facilities. And from February, the interval for other seniors will be shortened to seven months. The government says it has enough doses to meet demand.
Pfizer, Moderna vaccines approved
Japan had only approved the Pfizer vaccine for boosters when the rollout began on December 1. The Moderna vaccine was approved on December 16. The rollout is expected to gather pace, in part because people are able to choose which one they receive.
The government says it will use existing stockpiles, together with 170 million doses it will obtain next year from Pfizer and Moderna.
The dose in the Pfizer booster is the same amount as in the first two shots. But at 50 micrograms, Moderna’s booster is half the amount used in the initial two. Horiuchi Noriko, the state minister in charge of the rollout, says this could reduce the potential side effects of the Moderna vaccine.
The Moderna booster is available at vaccination venues that only used Pfizer’s for the initial two doses.
Study: mixing shots increases efficacy
According to Japan’s health ministry, a United States study of 458 people aged 18 and above found that mixing and matching the Pfizer, Moderna, and Johnson & Johnson vaccines is safe and highly effective.
The following points relate to the Pfizer and Moderna vaccines:
(Note: The study used 100 micrograms of the Moderna vaccine. Moderna boosters in Japan contain half that amount.)
- Three Moderna shots result in a 10.2-fold increase in antibodies 15 days after the booster.
- Three Pfizer shots result in a 20-fold increase.
- Two Pfizer shots and a Moderna booster result in a 31.7-fold increase.
- Two Moderna shots and a Pfizer booster result in an 11.5-fold increase.
This information is accurate as of December 22, 2021.