A contentious requirement for Japan-specific trials has delayed the rollout of Covid-19 vaccines in Asia’s largest advanced economy and threatened the Tokyo Olympics.

Small clinical trials that demonstrate the vaccines generate a similar level of antibodies when used in Japan are the main outstanding condition for approval of the jabs from BioNTech/Pfizer and several other companies.

Japan’s demand for proof that safety and efficacy do not differ in the country means that it will not start vaccinations until the end of February — three months after the earliest rollouts and fewer than five months before the delayed Tokyo Olympics are due to start.

Olympic organisers said they were working on the assumption that athletes who participate in the Games will not have been vaccinated by the summer.

Ken Ishii, professor of vaccine science at the University of Tokyo, said Japanese regulators were being “cautious rather than late” because they wanted to avoid an anti-vaccine backlash.

But he admitted the requirement was hard to justify scientifically. “To ask for an additional clinical trial with just 200 people doesn’t make much sense,” he said. “It doesn’t give you enough power to tell whether Japanese people are different.”

The Pfizer clinical trial involving more than 40,000 people in the US included 800 of Asian ethnicity, said Prof Ishii, and provided a better source of evidence for any genetic effect on safety or efficacy.

Japanese officials said that, as standard practice, vaccines developed abroad have to show they generate a similar level of antibodies when tested in local patients. They do not require further placebo-controlled trials to see how many patients catch Covid-19.

South Korea, which is also finalising its vaccine distribution plans, is running similar precautionary tests before starting mass inoculations in February.

“We will go through a review process to check the safety and efficacy of the Covid-19 vaccines on South Koreans, given the racial and ethnic differences,” Kim Hee-sung, a manager of the vaccine evaluation team at the Ministry of Food and Drug Safety told the Financial Times.

Last year, Japan agreed to buy 120m coronavirus vaccine doses from Pfizer, 120m from AstraZeneca and 40m from Moderna. Two doses are needed for each vaccination.

Pfizer has started a rolling submission for approval of its vaccine. It began a local trial in October and full results are expected imminently. AstraZeneca began local trials last summer and Japanese officials said they did not know why the company had not yet submitted its vaccine for approval.

Meanwhile, Moderna has only just begun its Japanese trial via local partner Takeda Pharmaceutical, so it is unlikely to submit its vaccine for several months.

That means Japan will rely heavily on BioNTech/Pfizer to roll out its vaccine campaign. The US company was contracted to supply all 120m doses by the end of June, but global demand is intense and the pace of deliveries to Japan is unclear.

Last week, Japan agreed a replacement contract with Pfizer, which will now supply 144m doses of its vaccine by the end of 2021.

Japan intends to vaccinate medical staff first, followed by the elderly. One official said the country’s annual influenza campaign — where it injects about 50m people over two months — would represent the upper limit on the pace of inoculations, but the Covid-19 rollout would probably be slower.

Local governments will mail out vouchers for Covid-19 injections to elderly citizens. Recipients will then be responsible for making their own appointments at vaccine clinics.

Hanging over Japan’s Covid-19 inoculation campaign is the nationwide rejection of vaccinations for human papillomavirus to protect against cervical cancer.

After a group of young women claimed the vaccine caused extreme neurological symptoms, the government stopped recommending it. Vaccination rates plunged to less than 1 per cent, compared with near-universal coverage in some European countries.

Polls show that only about 65 per cent of Japan’s population want the Covid-19 vaccine. Prof Ishii said that his task was to persuade the other 35 per cent.

“Everyone in Japan has to change their mentality. This is not a government problem, this is the people’s problem. We have to help the government to make it a success.”

Additional reporting by Song Jung-a and Edward White in Seoul