Ferdinands JM, Gaglani M, Ghamande S, et al. - Vaccine effectiveness for prevention of influenza-associated hospitalizations was determined among adults during the 2018-2019 influenza season. Cases were adults who admitted with acute respiratory illness to 14 hospitals of the US Hospitalized Adult Influenza Vaccine Effectiveness Network and tested positive for influenza; patients testing negative were assessed as controls. Data from 2,863 patients were analyzed. Findings suggested that vaccination conferred no protection against influenza A(H3N2)-associated hospitalizations despite that the risk of influenza-A(H1N1)pdm09-associated hospitalizations halved in correlation with vaccination. Researchers noted negative VE for young-and middle-aged adults, however, residual confounding as a potential explanation cannot be excluded.