Minor variant flu strains that escape detection by the the flu vaccine can be responsible for helping to spread it,  new research finds.

Influenza A virus, which causes the common flu, is a genetically diverse virus, which means its made up of a  lot of different strains.  Most of the scientific knowledge about the flu stems from the dominant strains, which are used in the making of vaccine to combat it.

An international research team led by scientists from New York University’s Department of Biology and College of Global Public Health  performed sophisticated genomic sequencing on upper nasal cavity swabs taken from confirmed cases of the 2009 flu pandemic in Hong Kong. They not only identified variants in flu strains, but also were able to quantify what was being transmitted between infected individuals.

Their results showed that, as expected, most carried the dominant virus--H1N1 or H3N2. But, in addition, all carried minor strains and variants of the major and minor strains not detected by the vaccine.

Not only are these major strains transmitted along with the major ones, but the study also that they replicate quickly and spread in ways not realized before, the researchers said in their study, which appears in Nature Genetics.