NHK has learned that laboratory tests in Japan show that two coronavirus vaccine shots are far less effective against the Omicron variant than the Delta variant.
A team led by Kitasato University Professor Katayama Kazuhiko measured levels of neutralizing antibodies in cultured cells taken from blood samples of 12 fully vaccinated people.
Neutralizing antibodies work as protection against a virus.
Six of the people had received two shots of the Pfizer vaccine and the rest were inoculated with the Moderna vaccine.
Levels of antibodies in the samples taken from people who got the second Pfizer shot three months ago were down 72 percent on average from the levels against Delta.
Levels in the samples from those who got the second Moderna shot three months ago were down 82 percent on average.
Professor Katayama says the findings in the lab experiment do not mean that vaccines are totally ineffective against Omicron.
He calls for fully vaccinated people to continue basic anti-infection measures.
Studies conducted overseas have also suggested that existing vaccines are far less effective against Omicron.