Does influenza vaccine supply affect racial disparities in vaccination among Medicare elderly?

Research Objective:

Some experts have expressed concern that existing racial disparities in influenza vaccination rates may worsen with vaccine shortages/delays. However, one past study exploring this issue did not support this concern (no change in disparities despite a vaccine supply disruption using cross-sectional analyses). To more precisely examine the effects of vaccine supply, we performed longitudinal analyses to assess changes in vaccination rate disparities during two consecutive seasons with differing levels of vaccine supply.

Study Design:

Using the Medicare Current Beneficiary Survey with claims, we performed longitudinal analyses using ordinary least squares models to examine whether the racial disparity changed during one season compared to the previous season in each of three periods. Each period includes one season with vaccine supply problems. Vaccine supply declined by 7.4 million doses between the 1999-2000 and 2000-01 seasons (Period 1); increased 7.3 million doses between 2000-01 and 2001-02 seasons (Period 2); declined 26 million doses between 2003-04 and 2004-05 seasons (Period 3). The outcome variable was: (1) if vaccinated in the first season but not second, (-1) if vaccinated in the second but not first, and (0) otherwise. Covariates were the changes in the cumulative number of vaccine doses distributed at the national level by December and influenza epidemic levels. Individual factors included were demographic and socio-economic characteristics, health status, and preference for health care. For time-invariant variables (e.g., race), an interaction term with the vaccine supply was created.

Population Studied:

Community-dwelling African American and white Medicare recipients aged 65 or older (weighted N = 5.64 million, 6.06 million, 6.63 million for Periods 1, 2 and 3, respectively).

Principal Findings:

When vaccine supply increased, as observed during the second season in Period 2, the disparity between African American and white elderly reduced by 8.6% (p<.05) compared to the previous season. This corresponds to an increase of one-million doses in supply reducing the black-white disparity by 1.1%. Conversely, when vaccine supply declined (Period 3), the black-white disparity increased by 8.3% (p =0.08) compared to the previous season. For Period 1, there was no disparity change between two seasons.

Conclusions:

Better vaccine supply was associated with reduced racial disparities in influenza vaccination rates, while worse supply increased racial disparities.

Implications for Policy, Delivery or Practice:

Distribution strategies that assure equal access to available vaccines for all citizens at all times could contribute to the Healthy People 2010 goal of eliminating disparities in immunizations.