The study, published in the journal PNAS, is based on a surveillance of pigs in China from 2011 to 2018, and found that the influenza virus strain, with genetic material termed as G4 genotype, has become predominant in swine populations since 2016.

Tokyo 2020 Olympics organisers and the International Olympic Committee have repeatedly said they have no contingency plans for the July 24-August 9 Summer Games since the WHO declared a global health emergency last month