Modified vaccines targeting new variants of the coronavirus won't require domestic clinical trials if the production process and handling of the shots are similar to those of the original authorized vaccine, the nation’s medicine regulator has said.

Drugmakers would still need to submit data from clinical trials overseas that shows immune response to the variants when they apply for Japanese approval, the Pharmaceuticals and Medical Devices Agency (PMDA) said in a statement this week.

That could significantly speed up the nation's lengthy approval process and allow for the smooth rollout of vaccines targeting more contagious and deadly variants.

The National Institute of Infectious Diseases estimated that new variants were responsible for about 70% of new COVID-19 cases confirmed in Osaka and Hyogo prefectures earlier this month, which likely pushed up a recent surge in infections. That compared with about 10% in Tokyo, Kanagawa and Chiba prefectures, but the government is worried that there could be a spike in the greater Tokyo area as well.

Japan was the last Group of Seven nation to approve its first coronavirus vaccine in February due to its requirement that an additional clinical trial be conducted on Japanese people to ensure safety. The U.K. and the U.S. approved the Pfizer Inc. shot, jointly developed with Germany’s BioNTech SE, two months earlier.

The PMDA last September had said new coronavirus vaccines developed by foreign drugmakers would need to go through a clinical trial in Japan, in principle. But the possibility that vaccines modified to counter new strains could be approved without large clinical trials has been gaining traction among drug regulators around the world.

The U.S. Food and Drug Administration said in February that vaccines adapted to fight coronavirus variants do not have to undergo large clinical trials and added that data from small clinical trials like those required in the process for annual flu vaccines would need to be submitted for approval instead.

The PMDA’s shift in its stance comes as COVID-19 cases linked to the new variants first identified in South Africa, the U.K. and Brazil have been spreading quickly at home and abroad, leading to a wave of severe cases and deaths in much of the world. Pfizer and other pharmaceutical companies have been accelerating the development of updated vaccines amid rising concerns that the virus may be mutating fast enough to evade the protection provided by the original vaccines, which would dash hopes for an early return to normalcy.

Late-stage trials of Pfizer’s vaccine conducted in the U.S. and five other countries on more than 43,000 participants, of which 5% were Asian, showed that it was 95% effective in preventing COVID-19. But laboratory experiments have pointed to a lower efficacy against the variant first detected in South Africa, known as B.1.351.

BioNTech and Pfizer have said they could develop a new shot to counter a new variant within six weeks. They have also been discussing a clinical study on a modified vaccine based on the B.1.351 variant with the U.S. Food and Drug Administration and other regulators.

Moderna Inc. has shipped doses of a variant-specific vaccine candidate against B.1.351 for a Phase 1 clinical trial in February. British drugmaker AstraZeneca PLC has also been studying a modified vaccine after its original shot was found to have only 10.4% efficacy against the South African variant last month.

The new variants have dozens of mutations, including genetic changes in the spike protein that the coronavirus uses to infect human cells. According to the European Center for Disease Prevention and Control, mutations in the new variants relate to the receptor binding site, which may alter the antigenic properties of the virus, and that it is likely that some reduction in neutralization by antibodies will be seen. Some experts have warned that the coronavirus could "outsmart" the vaccines sooner or later.

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