Politically weakened by criticism over his coronavirus response, Prime Minister Yoshihide Suga is pinning his hopes of remaining in power on the successful rollout of vaccines across Japan.

Suga has put vaccines front and center in his messaging to the public over the past month, calling them the "decisive factor" for bringing the pandemic under control and appointing Taro Kono, the outspoken and popular reform minister, as his vaccine czar.

According to government officials, the prime minister repeatedly pushed the Ministry of Health, Labor and Welfare in recent weeks to speed up the process to begin administering the vaccine developed by drugmaker Pfizer Inc. and its partner BioNTech SE.

The first shipment of the vaccine arrived in Japan on Friday, two days ahead of schedule. After fast-track approval for its domestic use on Sunday, the country is set to start inoculating health workers this week, earlier than late February as previously planned.

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A senior administration member called the vaccine a "lifeline" for Suga, whose Cabinet approval rating fell to 38.8 percent in a Kyodo News poll this month, compared with 66.4 percent when he took office in September last year.

Suga is expected to call a general election by dissolving the House of Representatives sometime before October, when the current four-year term of lower house members ends. The prime minister must quickly get the public back on his side if he is to maintain support within the ruling Liberal Democratic Party.

Distribute vaccines to Japan's population of 126 million, revive the economy, and host a successful Tokyo Olympics and Paralympics. "It's the only scenario for the prime minister to regain momentum," said a senior LDP official.

But while Suga has pledged to get the vaccine, which in clinical trials was 95 percent effective in preventing COVID-19, to the public "as soon as possible," the country has already fallen behind in administering shots.

The United States and the European Union both approved and began distributing the Pfizer vaccine in December, and the latter's new export controls could mean subsequent shipments to Japan may be delayed.

It could also take several more months to screen vaccines developed by AstraZeneca Plc and Moderna Inc., the other two drugmakers with which the health ministry has supply contracts.

Adding to Suga's woes, opposition parties are taking aim at allegations his eldest son wined and dined officials at the Ministry of Internal Affairs and Communications, which in 2018 granted a license to his employer, satellite broadcasting firm Tohokushinsha Film Corp.

The resignation of former Prime Minister Yoshiro Mori as head of the Tokyo Olympics organizing committee over sexist remarks has also dented the administration's hopes that a successful Summer Games will buoy Suga's popularity.

The public is already skeptical that the Olympics and Paralympics can go ahead during a pandemic, with the Kyodo News poll showing more than 80 percent think they should be postponed again or canceled outright.

Masahiro Iwasaki, a political science professor at Nihon University, said Suga is already on his last legs and may be ousted if the LDP loses by-elections on April 25 to fill parliamentary seats in Hiroshima and Nagano prefectures, having already chosen not to field a candidate in Hokkaido.

"Starting vaccinations may help a little bit, but there really isn't much else working in his favor at this point," Iwasaki said.