Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance

Huang, Qiu Sue; Turner, Nikki; Baker, Michael G; Williamson, Deborah A; Wong, Conroy; Webby, Richard; Widdowson, Marc-Alain

Influenza vaccine strain selection requires annual consultations and frequent updates to match the antigenic drift of the circulating viral strains, and ample evidence indicates that influenza vaccine effectiveness (VE) varies not only by virus type (subtype) but also from year to year. 32, 33 Robust and timely vaccine effectiveness estimates are important to measure the public health benefit of seasonal influenza control strategies, pandemic preparedness and vaccine strain selection. 34 Many VE estimates derive from observational studies with existing data collecting systems which often have multiple limitations and biases, and there are international calls for more rigorous VE studies. [34] [35] [36] [37] [38] [39] SHIVERS is providing robust and timely estimations of the protective effect of seasonal influenza vaccine in the prevention of hospitalizations and general practice consultations for laboratory-confirmed influenza using case test-negative control methods. 40, 41 Immune response An individual's immune response to influenza infection can vary depending on many factors (e.g. age, underlying conditions and ethnicity). Clinical observation during the 2009 pandemic indicated that the unexpected low morbidity and mortality rates in the elderly were in part due to their crossreactive immunity. 3, 42, 43 There are knowledge gaps regarding each component of adaptive immune responses in determining an individual's risk of acquiring influenza virus infection and the severity of the resulting disease: antihemagglutinin (HA) antibodies, antineuraminidase (NA) antibodies, isotypes of responding antibodies, influenza-specific CD4+, CD8+ T cells, surface markers and key cytokines. 44, 45 Additionally, there are scarce data on the correlation of cellular immunologic and neuraminidase targeted antibody responses in individuals with serologically (anti-HA antibodies) defined influenza infection. 46, 47 By interconnecting the epidemiological and immune studies in severe and moderate disease cases and high-risk subgroups (e.g. Pacific and Maori ethnic groups) and individuals with serologically defined influenza infection, SHIVERS will facilitate our understanding of host immune responses that determine an individual's risk of acquiring influenza infection or developing severe disease.