Japan has begun a study on whether it should administer third shots of the coronavirus vaccine next year, officials said Friday.

Spurred by the likelihood of vaccine efficacy waning over time and the need to respond to highly infectious virus variants, the government will proceed with the study while trying to secure the supply of at least 200 million doses next year, the officials said.

Tokyo will reach a decision on the matter after taking into consideration the situation of virus infections and how other governments are dealing with COVID-19 booster shots.

Overseas, Israel's booster shots have already been in full swing for people aged 60 or older, while Germany is scheduled to start providing third COVID-19 shots for the elderly in September. Sweden has also decided to do likewise, possibly in the fall, with Britain preparing to start offering booster shots in September.

Japan's vaccination program was launched in February, initially for health care workers. It was expanded to the elderly in April and later to other members of the public.

The country's minister in charge of vaccination efforts, Taro Kono, said July 30 Japan "will likely administer next year" third doses of COVID-19 vaccine.

The government struck a contract in July to receive an additional 50 million doses of Moderna Inc.'s coronavirus vaccine from the beginning of 2022. Discussions are also under way to secure 150 million doses of the vaccine developed by Novavax Inc. starting in early 2022.

As judgment on the necessity of booster shots varies among nations, Japan will collect data on clinical trials conducted abroad and study not only on the necessity but also whether it should allow a person's third dose to be from a different company than the one that developed their first and second doses, the officials said.

On Thursday, Moderna said its coronavirus vaccine maintained 93 percent efficacy through six months after the second shot, but pointed to the likelihood of the need for a third booster shot afterward to protect against new variants, citing a decline in antibody levels.

Meanwhile, World Health Organization chief Tedros Adhanom Ghebreyesus on Wednesday called on some advanced countries to suspend their ongoing or planned administration of third shots until at least the end of September, saying fair access to COVID-19 vaccines among all countries is a higher priority.

Noting that many people must work to make a living even amid the pandemic, the WHO chief told a press conference, "While hundreds of millions of people are still waiting for their first dose, some rich countries are moving towards booster doses."