TOKYO (REUTERS) - Japan is making an aggressive move to grab enough coronavirus vaccine to inoculate its population four times over, a push the government hopes will instil confidence that it can host a delayed summer Olympics next year.

Like other rich countries, Japan is signing multiple deals because some of the vaccines could fail in clinical trials or require more than one dose, an approach some experts consider prudent.

But Japan has something else riding on a successful mass roll-out of a vaccine: Prime Minister Shinzo Abe's enduring aim to bring thousands of athletes and fans to Tokyo for the Games in 2021, after the event fell through this year due to the pandemic.

Chief Cabinet Secretary Yoshihide Suga, the top government spokesman, said Japan was working with Olympic organisers on how to go ahead with the Games, tying the effort to the need to secure a vaccine.

The various companies "will probably be able to produce a vaccine between the end of this year and next March", Mr Suga told Reuters in an interview this week.

"There are a lot of considerations, but we want to hold the Olympics at all costs."

Japan is on track to have 521 million doses of five different vaccines in 2021, compared with a population of 126 million.

Recent deals include global arrangements with such drugmakers as Pfizer and AstraZeneca, as well as local deals with the likes of Shionogi & Co.

"You have to bet evenly to avoid getting nothing," said Dr Tomoya Saito, director at Japan's National Institute of Public Health.

Some critics contend that Japan's rush to secure supplies is driven largely by a political desire to show the world it is fully committed to hosting the Games.

"The plan is, hope for a miracle and then capitalise on that miracle," said Professor Michael Cucek, a political science expert at Temple University Japan.

"But the time frame for that is getting narrower and narrower."

Health ministry and Cabinet Office officials did not respond to queries about whether Japan's drive to secure coronavirus vaccines was connected to the Olympics.

Japanese officials have discussed putting on a "simplified" Games, originally expected to attract 600,000 visitors.

But the event would still involve some 11,000 athletes from around the world.

Given the size of the events and people coming from all over the world, holding the Olympics require "mass quantities of an effective vaccine," said Professor Kenji Shibuya, director of the Institute of Population Health at King's College, London.

Staging an Olympics in a pandemic will be a huge logistical challenge, as thousands of athletes around the world will have to train and travel to events and many more thousands of fans will have to be accommodated at a time when many countries may still be in lockdown.

Japan still has a travel ban in place covering more than 140 countries.

Even with a viable vaccine, the additional challenge of immunising athletes and visitors before or after landing in Japan will be enormous.

A "very, very essential factor" for the Olympic hosts will be when an effective vaccine will be ready and how it will be distributed, Tokyo Governor Yuriko Koike told Reuters on Tuesday (Aug 25).

"We will do our best to prevent coronavirus infections here in Japan and also to welcome the athletes from all over the world."