TOKYO (REUTERS) - Japan's Covid-19 vaccine chief has blamed a rigid drug approval system for a slow inoculation campaign that is relying on only one approved shot, as a fourth wave of infections raises worries amid preparations for the Summer Olympics.

Mr Taro Kono, the minister in charge of vaccines, took responsibility for the public frustration with the vaccine distributed system but also said the approval process was a disadvantage in an emergency.

"Even though we are in a state of crisis, we're still using the same rules to approve vaccines that we do under normal times," Mr Kono said in a TBS television interview broadcast on Wednesday (May 12).

"In the wake of this corona situation, the administration needs to change." The government aims to inoculate most of its 36 million people over the age of 65 by the end of July.

The Olympics, postponed last year as the virus was spreading around the world, are due to begin on July 23.

To reach that vaccination target, the government hopes to deliver about one million shots a day, about three times faster than the current pace.

From early in the crisis, the government has said it would not skip regulatory steps to ensure the safety and efficacy of vaccines. That means domestic clinical trials and reviews taking several months to complete.

Some other countries have introduced emergency approvals to deploy vaccines faster.

Japan approved the vaccine developed by Pfizer and BioNTech, in mid-February, two months later than in the United States.

The delay, along with a host of logistical problems, has meant Japan has inoculated just 2.9 per cent of its population, the lowest rate among wealthy countries.

Pfizer started its Japan trial in October last year, recruiting 160 volunteers to take its vaccine. AstraZeneca, which is still being considered by domestic regulators, started its vaccine trial earlier with 256 subjects.

But trials involving such small numbers of people are "really meaningless", said Dr Takahiro Kinoshita, a Japanese physician and researcher based in Boston.

Global trials involve enough Asian subjects to ensure safety in their genotype, Dr Kinoshita said.

Japan's trials, lengthy reviews and slow roll-outs stem from public fears about vaccines that have undermined previous inoculation campaigns for human papillomavirus and other diseases.

"Everything is connected to vaccine hesitancy behaviour," he said.

The Health Ministry and the Pharmaceuticals and Medical Devices Agency, Japan's main drug regulator, did not immediately respond when contacted for comment on Mr Kono's remarks.

About 75 per cent of Japanese are dissatisfied with the vaccine roll-out and Japan had the lowest rates of approval of government handling of the pandemic among six major economies in a survey by global consultancy Kekst CNC released on Wednesday.