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Introduction CDC's Advisory Committee on Immunization Practices (ACIP) provides annual recommendations for the prevention and control of influenza. The ACIP Influenza Vaccine Working Group* meets monthly throughout the year to discuss newly published studies, review current guidelines, and consider potential revisions to the recommendations. As they review the annual recommendations for ACIP consideration, members of the Working Group consider a variety of issues, including vaccine effectiveness, safety and coverage in groups recommended for vaccination, feasibility, cost-effectiveness, and anticipated vaccine supply. Working Group members also request periodic updates on vaccine and antiviral production, supply, safety and efficacy from vaccinologists, epidemiologists and manufacturers. State and local immunization program representatives are consulted. Influenza surveillance and antiviral resistance data were obtained from CDC's Influenza Division. The Vaccines and Related Biological Products Advisory Committee of the Food and Drug Administration (FDA) selects the viral strains to be used in the annual trivalent influenza vaccines. Published, peer-reviewed studies identified through literature searches are the primary source of data used in making these recommendations. Among studies discussed or cited, those of greatest scientific quality and those that measured influenza-specific outcomes were the most influential during the development of these recommendations. For example, population-based estimates that use outcomes associated with laboratory-confirmed influenza virus infection contribute the most specific data for estimates of influenza burden. The best evidence for vaccine or antiviral efficacy and effectiveness studies comes from randomized controlled trials that assess laboratory-confirmed influenza infections as an outcome measure and consider factors such as timing and intensity of influenza circulation and degree of match between vaccine strains and wild circulating strains (9,10). Randomized, placebo-controlled trials cannot be performed in populations for which vaccination already is recommended, but observational studies that assess outcomes associated with laboratory-confirmed influenza infection can provide important vaccine effectiveness data. Randomized, placebo-controlled clinical trials are the best source of vaccine and antiviral safety data for common adverse events; however, such studies do not have the power to identify rare but potentially serious adverse events. The frequency of rare adverse events that might be associated with vaccination or antiviral treatment is best assessed by retrospective reviews of computerized medical records from large linked clinical databases, with chart review for persons who are identified as having a potential adverse event after vaccination (11,12). Vaccine coverage data from a nationally representative, randomly selected population that includes verification of vaccination through health-care record review is superior to coverage data derived from limited populations or without verification of immunization but is rarely available for older children or adults (13). Finally, studies that assess immunization program practices that improve vaccination coverage are most influential in formulating recommendations if the study design includes a nonintervention comparison group. In cited studies that included statistical comparisons, a difference was considered to be statistically significant if the p-value was <0.05 or the 95% confidence interval (CI) around an estimate of effect allowed rejection of the null hypothesis (i.e., no effect). These recommendations were presented to the full ACIP and approved in February 2007. Modifications were made to the ACIP statement during the subsequent review process at CDC to update and clarify wording in the document. Data presented in this report were current as of June 27, 2007. Further updates, if needed, will be posted at CDC's influenza website (http://www.cdc.gov/flu). |