Effects of an ongoing epidemic on the annual influenza vaccination rate and vaccination timing among the Medicare elderly: 2000-2005.

OBJECTIVES

We assessed short-term responsiveness of influenza vaccine demand to variation in timing and severity of influenza epidemics since 2000. We tested the hypothesis that weekly influenza epidemic activity is associated with annual and daily influenza vaccine receipt.

METHODS

We conducted cross-sectional survival analyses from the 2000-2001 to 2004-2005 influenza seasons among community-dwelling elderly using the Medicare Current Beneficiary Survey (unweighted n = 2280-2822 per season; weighted n = 7.7-9.7 million per season). The outcome variable was daily vaccine receipt. Covariates included the biweekly changes of epidemic and vaccine supply at 9 census-region levels.

RESULTS

In all 5 seasons, biweekly epidemic change was positively associated with overall annual vaccination (e.g., 2.7% increase in 2003-2004 season) as well as earlier vaccination timing (P < .01). For example, unvaccinated individuals were 5%-29% more likely to receive vaccination after a 100% biweekly epidemic increase.

CONCLUSIONS

Accounting for short-term epidemic responsiveness in predicting demand for influenza vaccination may improve vaccine distribution and the annual vaccination rate, and might assist pandemic preparedness planning.