Factors associated with influenza vaccination failure and severe disease in a French region in 2015.

Flu virus is mutating into other strains and the vaccine has not been sufficiently attenuated, with the result that there was a 3-fold increase in flu.

See study: PLoS One. 2018 Apr 17;13(4):e0195611. doi: 10.1371/journal.pone.0195611. eCollection 2018.  https://www.ncbi.nlm.nih.gov/pubmed/29664931