Around 90 percent of those who received the vaccine developed by U.S. pharmaceutical giant Pfizer Inc. were found to have antibodies against the various COVID-19 variants detected in Japan, a university study showed Wednesday.

The study by a research team at Yokohama City University was conducted on 105 people who had received both doses of the vaccine without contracting the novel coronavirus and covered seven variants.

Photo shows vials of Pfizer Inc.'s COVID-19 vaccine at a hospital in Iwamizawa, Hokkaido, northern Japan, on Feb. 19, 2021. (Kyodo) ==Kyodo

Of the 105 people, 90 to 94 percent were found to have antibodies against the variants found in Britain, South Africa and Brazil, while 97 percent had antibodies against the variant detected in India, the study showed.

It also found that 99 percent had antibodies against the coronavirus present from the start of the outbreak in Japan.

The vaccine developed by Pfizer and German partner BioNTech SE is currently the only one authorized for use in Japan.

Japan is now facing a fourth wave of infections amid the spread of more contagious variants, while its vaccine rollout is lagging behind other countries, such as Britain, Israel and the United States.

In a study submitted to the health ministry on Wednesday, the National Institute of Infectious Diseases said the so-called N501Y variant is likely to have replaced more than 90 percent of strains without mutations in Japan.

The coronavirus variant is around 1.4 times more likely than the original strains to cause serious symptoms such as pneumonia by the time an infected individual is diagnosed with COVID-19, it said.

Yokohama City University Professor Takeharu Yamanaka speaks during a press conference in Tokyo on May 12, 2021. (Kyodo)