SYDNEY—Australian researchers who have spent much of the past two years studying Covid-19 recently turned their attention to another public-health mystery: the possible disappearance of one of the four main strains of flu that infect humans.
Around the world, labs that use genetic sequencing to determine which flu strain has sickened a patient upload their findings to an international database known as GISAID. Since early last year, none of those labs have confirmed the presence of the influenza B Yamagata lineage, the technical name for one of the four strains.