Impact of the 2004 influenza vaccine shortage on repeat immunization rates.

Purpose: We assessed the impact of the severe influenza vaccine shortage of 2004 on individual physicians' immunization performance.

Methods: Using 1998-2004 Medicare claims data, we monitored the physician continuity rate (proportion of patients receiving influenza immunization from a physician in 1 year who received a subsequent immunization from the same physician the subsequent year) and other clinician rate (proportion of patients with claims from 1 physician in 1 year with a claim from another clinician the subsequent year) in West Virginia Medicare beneficiaries from 2000-2004. We examined vaccine claim trends by clinician and surveys of self-reported immunization to determine whether patients received vaccine from nonphysician clinicians or went without immunization each year.

Results: Claims-based influenza vaccination rates increased from 35.5% to 41.3% from 2000-2003, reflecting historical trends, before declining 14.1% in 2004. Median continuity rates among the 723 to 849 physicians claiming 25 or more influenza immunizations from 2000-2003 increased from 47% in 2000-2001 to 54% in 2002-2003; then fell to 3% in 2003-2004. The number of physicians filing 100 or more claims declined from 337 in 2003 to 130 in 2004. More than 25% of physicians had no repeat vaccinations of the same beneficiaries in 2004. Trends in clinician type and survey data indicated a shift of many beneficiaries to mass vaccinators and institutional providers; however, compared with previous years, there was an estimated 8% increase in 2004 in the number of West Virginia beneficiaries who did not receive vaccine.

Conclusions: The 2004 vaccine shortage had a severe impact on influenza immunization rates in private physician's offices, disrupting continuity of care.