Moderna Inc's COVID-19 vaccine is unlikely to win approval in Japan until May due to requirements for local clinical trials, the distributor said, casting doubt over a nationwide vaccination rollout before the Tokyo Olympics.

With an eye on the Olympics due to start in late July, Japan has secured rights to at least 540 million doses of COVID-19 vaccines from several Western developers, the biggest quantity in Asia and more than enough for its 126 million population.

But Tokyo faces a major regulatory bottleneck due to requirements for local clinical trials before requesting approval. Several other countries have fast-tracked the review process to expedite mass inoculations.