Influenza vaccine overview: Summary and assessment. Issue Brief
Immunization tops the list of the 10 great public health achievements during the last century (Centers for Disease Control and Prevention [CDC], 1999a). Despite this achievement, each year less than half of those who are at highest risk for influenza-related complications are vaccinated. Meanwhile, influenza is the leading cause of mortality due to infectious disease (CDC, 2005a), causing an average of 36,000 deaths (Thompson et al., 2003) and 226,000 hospitalizations annually (Thompson et al., 2004).
The capacity of the health care delivery system to accommodate the demand for influenza vaccine depends largely on a combination of factors that shift from year to year, including the virulence of the circulating influenza strains, the ability of manufacturers to match a vaccine to these strains, and the timeliness of vaccine distribution. Moreover, influenza immunization is unique when compared to other types of immunizations for several reasons:
- The influenza vaccine is reformulated each year in an attempt to match the strain(s) of the virus anticipated to circulate in the coming season.
- Because it is reformulated annually, the influenza vaccine has a limited shelf life.
- The influenza vaccine is typically administered prior to the start of the influenza season (approximately October to early December).
- Various factors related to the marketplace and supply chain affect the timely and efficient distribution of influenza vaccines.