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Countries that have secured vaccines for the coronavirus have been forced to make a hard choice: give two shots that will guarantee a higher efficacy, or give one shot to as many people as possible.

Japan, for now, is going with the two-shot option, but that could change if it cannot secure a sufficient supply of vaccines or if it becomes evident that a single shot is enough for a high degree of efficacy.

“If there’s strong efficacy even with one dose and that became the way to go in Japan, the (vaccination) method would change,” Taro Kono, the minister in charge of the vaccine rollout, told NHK on Sunday, indicating that the government will consider prioritizing single shots in a possible reversal of the current two-dose strategy.

The vaccine czar’s comments come after an Israeli hospital’s study found that the first dose of Pfizer Inc.’s vaccine, developed jointly with BioNtech SE, reduced COVID-19 symptoms by up to 85%, slightly lower than the 95% efficacy confirmed for two shots in late-stage clinical trials. A separate study showed that a single dose of the vaccine developed by the University of Oxford and British-Swedish drugmaker AstraZeneca PLC provided 76% protection in the first 90 days after vaccination.

The U.K. has decided to prioritize giving single vaccine shots so more people will be reached as quickly as possible, and it has extended the interval between jabs from three to four weeks to up to 12 weeks, a strategy that has paid off in reducing infections, serious symptoms and deaths.

But health minister Norihisa Tamura says Japan will stick to the standard two-dose schedule with a three-week interval between jabs for Pfizer’s vaccines, a view echoed by Prime Minister Yoshihide Suga during a meeting with Natsuo Yamaguchi, the head of the coalition partner of the ruling Liberal Democratic Party on Wednesday.

“The effectiveness for preventing the onset of symptoms would fall to some extent compared with two doses,” Tamura said at a news conference Wednesday, commenting on the single-shot option. “The duration of how long antibodies last would also get shorter, so for now, we’re not considering a single shot yet.”

Japan’s coronavirus vaccine rollout finally kicked off last week, two months behind the U.K. and the U.S., but Kono has been unable to give a detailed rollout schedule, as Pfizer’s vaccines, which are exported from its factory in Belgium, have been subjected to European Union export controls on vaccines produced within the bloc.

Japan has so far received two shipments of Pfizer’s vaccines, amounting to almost 840,000 shots, but there is no timetable for the third shipment yet amid the intensifying global race to secure supply. Japan is hoping to procure enough shots for all residents under the current two-shot regimen by the end of June. But on Monday, a number of the ruling LDP lawmakers backed emulating single-shot approaches at the party’s vaccine project team meeting amid expectations that more lives could be saved.

Dr. Tetsuo Nakayama, a project professor at the Kitasato Institute for Life Sciences and director of the Japanese Society of Clinical Virology, says that the protracted vaccine shortage could justify providing one dose to many people as soon as possible.

“It depends on the level of supply,” Nakayama said. “If there’s a lack of supply, one shot may become inevitable, but considering that the antibodies are low with a single shot and there’s no data on how long the antibodies last after a single shot, a two-dose regimen would be best if there’s an adequate supply.”

After inoculating 40,000 heath care workers who work mostly at state-run hospitals, vaccinations for 4.7 million other health care workers are set to begin by the end of the month. Kono has said the government plans to distribute 2.34 million vaccines for 1.17 million people, but that would be only a quarter of what’s needed to vaccinate the health care workers.

Amid the slow pace of Pfizer’s vaccine exports, the pending approval of two other vaccines that Japan plans to procure — those developed by AstraZeneca and U.S. pharmaceutical firm Moderna Inc. — is gaining keen attention. AstraZeneca filed for fast-track approval of its vaccine with the health ministry on Feb. 5 and plans to submit clinical data from its domestic trial next month, with formal approval expected as early as March.

AstraZeneca, which has signed a contract to supply 120 million doses to Japan, is expected to export 30 million shots to the nation by the end of March and is considering manufacturing the remainder in Japan by taking advantage of subsidies, the government has said. On the other hand, the Moderna vaccine’s approval is seen as unlikely before May.

Additional reporting by contributing writer Eriko Yamakuma

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