A survey by Japanese researchers suggests that two shots of a coronavirus vaccine have a 95-percent efficacy rate in protecting the recipients from infection.

Japan's National Institute of Infectious Diseases presented the preliminary results of its survey at a meeting of health ministry experts on Wednesday.

A group of researchers surveyed 1,130 people who developed a fever and visited one of five medical facilities in Tokyo in June and July.

They say that 350 of the 914 people who had not been vaccinated, and 46 of the 141 who had received one shot of the Pfizer or Moderna vaccine, tested positive for the coronavirus. They found that 3 of the 41 people who had a second vaccination also tested positive.

Based on the results, the group estimates that one vaccine shot is 48 percent effective against the coronavirus, and the efficacy rate rises to 95 percent two weeks after a second jab.

The institute says its preliminary data is almost identical to the results of studies in other countries.