Health workers were given Japan’s first coronavirus shots on Wednesday, launching a vaccination programme deemed crucial to hosting the already postponed Tokyo Olympics.

However, in a nation worried about potential shortages of imported vaccines and where people are often hesitant to take vaccines due to fears about side effects, the impact the campaign could make is uncertain.

The massive push comes after the government gave its delayed first Sunday approval for shots produced and supplied by Pfizer, which have been used since December in many other countries.

In addition to the company’s earlier studies in six other nations, Japan fell behind after it requested Pfizer to perform clinical tests with Japanese individuals. But officials claim it was important to answer many Japanese fears about safety in a country that is notorious for its low trust in vaccines.

Owing to supply shortages and limitations in Europe, where many are produced, stocks of imported vaccines are a major concern. The availability of imported vaccines will decide the success of the Japanese vaccination campaign, Vaccine Minister Taro Kono said on Tuesday.

About 40,000 doctors and nurses got their first shots from 100 selected hospitals around the country on Wednesday, with a second shot scheduled for March 10. Half will engage in a health survey lasting 7 weeks.

Japan’s inoculation programme is running on a tight schedule, after weeks of delay.

Vaccines arrived at a hospital in Tokyo late Tuesday, the night before inoculations began on Wednesday morning for their employees.

The first Pfizer vaccine shipment that arrived last Friday is enough for 40,000 doctors and nurses from 100 selected hospitals across the country, Kono said.

Inoculations will commence in March with 3.7 million more health staff, followed by about 36 million people aged 65 and older beginning in April. Before the general public has its turn, individuals with chronic health conditions, as well as staff at nursing homes and other facilities, would be next.

It would be around June by the time average citizens have their turn, and it will be difficult to achieve so-called “herd immunity” against the virus before the Olympics, experts claim.

The 2020 Olympics in Tokyo are due to commence in July.

Japan’s vaccine mistrust is decades old. Most individuals have a vague fear about vaccines, in part because their side effects have also been replicated.

For seven weeks, half of the recipients of the first shots will maintain regular reports of their condition, data that will be included in a clinical survey to tell people concerned about the side effects.