Since states’ public health systems differ as to pandemic preparedness, this study explored whether such heterogeneity among states could affect the nation’s overall influenza rate.

The CDC produced a uniform set of scores on a 100-point scale from its 2008 national evaluation of state preparedness to distribute materiel from the Strategic National Stockpile (SNS). This study used these SNS scores to represent each state’s relative preparedness to distribute influenza vaccine in a timely manner and assumed that “optimal” vaccine distribution would reach at least 35% of the state’s population within 4 weeks. The scores were used to determine the timing of vaccine distribution for each state: each 10-point decrement of score below 90 added an additional delay increment to the distribution time.

A large-scale agent-based computational model simulated an influenza pandemic in the U.S. population. In this synthetic population each individual or agent had an assigned household, age, workplace or school destination, daily commute, and domestic inter-city air travel patterns.

Simulations compared influenza case rates both nationally and at the state level under three scenarios: no vaccine distribution (baseline), optimal vaccine distribution in all states, and vaccine distribution time modified according to state-specific SNS score.

Between optimal and SNS-modified scenarios, attack rates rose not only in low-scoring states but also in high-scoring states, demonstrating an inter-state spread of infections. Influenza rates were sensitive to variation of the SNS-modified scenario (delay increments of 1-day versus 5-days), but the inter-state effect remained.

The effectiveness of a response activity such as vaccine distribution could benefit from national standards and preparedness funding allocated in part to minimize inter-state disparities.