Japanese researchers say vaccines targeting Omicron coronavirus variants are 71 percent effective in preventing infections.

Scientists at the National Institute of Infectious Diseases and other researchers compared vaccination records of about 4,000 people aged 16 or older who took virus tests at 10 medical facilities in the Kanto region.

The samples were taken between September and November, when the Omicron's BA.5 subvariant was the dominant strain.

The results show Omicron-targeting vaccines were 71 percent effective among those who had been at least twice inoculated with a conventional vaccine before taking an Omicron-specific booster.

More specifically, vaccines targeting the BA.1 subvariant proved 73 percent effective, while shots for BA.4 and BA.5 subvariants were found to be 69 percent effective.

The researchers say there was no significant difference between the two kinds of Omicron-targeting vaccines in their capabilities to prevent infections.

They are now planning to look into how long these vaccines remain effective.