Low influenza vaccine effectiveness and the effect of previous vaccination in preventing admission with A(H1N1)pdm09 or B/Victoria-Lineage in patients 60 years old or older during the 2015/2016 influenza season

Our findings indicate that IVE was low in preventing A(H1N1)pdm09 and strongly correlated with vaccination in the previous season. No effect in preventing admission with B/Victoria-lineage was observed. For the 2015/2016 season, IVE was low due to a mismatch and lack of concordance between the circulating and vaccine viruses.