Japan expects to receive 50 million additional doses of Pfizer Inc.'s COVID-19 vaccine after Prime Minister Yoshihide Suga called on the pharmaceutical firm to boost supplies, government sources said Wednesday.

Together with existing agreements with Pfizer for 144 million doses and Moderna Inc. for 50 million doses, Japan is now set to procure enough vaccine for the roughly 110 million people aged 16 or older.

Suga reiterated in a parliamentary session that the government expects to have supplies to cover everyone eligible by the end of September after requesting the additional doses in a phone call with Pfizer CEO Albert Bourla on Saturday.

But he declined to say how many additional doses were on the way or how much Japan would pay for them.

Japan's vaccine rollout has lagged behind other countries including Britain and the United States, held up by its slow approval process as well as early production delays at Pfizer's factory in Belgium and the European Union's export controls.

A little over 1.2 million health care workers and around 19,000 people aged 65 or older had received at least one of the two required shots as of Monday, according to government data, around 1 percent of the country's population.

Suga denied the claim by a senior member of his Liberal Democratic Party that it could take until the end of this year and possibly even part of next year to finish vaccinating the country's elderly, saying the government has received no such information from municipalities.

After people aged 65 and older, those with underlying conditions such as diabetes and workers at elderly care facilities are set to get their shots before the rest of the population.

The Ministry of Health, Labor and Welfare has only approved the Pfizer vaccine so far, with the Moderna vaccine expected to be given the green light as early as next month.

Japan also has a supply agreement with AstraZeneca Plc for 120 million doses, but the approval process could be held up by overseas reports of rare cases of blood clots.