 In various clinical studies the investigators demonstrated that the immune response against the influenza A viruses is improved as a result of the higher hemagglutinin content. Furthermore, influenza virus disease and hospitalization associated with influenza-related illness in older adults 50 years was considerably reduced 90 following vaccination with TIV, even though the circulating influenza A strain was antigenically dissimilar to that in the vaccine. However, more recently Skowronski et al. reported that the low influenza vaccine effectiveness in 2012-2013 was not associated with antigenic drift but was instead related to mutations in the egg-adapted H3N2 vaccine strain. Flublok manufactured using recombinant technology does not contain the mutations responsible for the reported lower effectiveness and may thus offer improved protection when mutations such as those described are induced in the process of adapting the influenza virus to growth in eggs. 