Using a conceptual framework adapted from Diderichsen et al. (14), we systematically considered possible sources of disparities during an influenza pandemic by examining the following 3 levels at which underlying socioeconomic or racial/ethnic differences could lead to disparities in illness or death: 1) likelihood of being exposed to the influenza virus; 2) likelihood of contracting influenza disease, if exposed; and 3) likelihood of receiving timely and effective treatment after influenza disease has developed. To explore socioeconomic and racial/ethnic disparities at each level, we searched the literature for relevant findings based on population-based national data (Figure, Table).

Although reducing or eliminating socioeconomic and racial/ethnic disparities in health and healthcare has been an official federal and state policy priority for 2 decades (34), such disparities remain prevalent and may inadvertently become wider when not explicitly addressed by policies designed to improve the health of the population as a whole and of disadvantaged persons in particular (35). Given the current limitations of our public health infrastructure and the disparities in healthcare, a pandemic influenza outbreak in the United States is likely to disproportionately affect persons from socially disadvantaged groups. Explicit, systematic, and detailed plans are essential for overcoming the social barriers that are predicted to result in socioeconomic and racial/ethnic disparities in pandemic influenza illness and death. Saunders and Monet also have called for pandemic influenza planning that appropriately considers the needs of disadvantaged populations (36).

The Pandemic Influenza Plan of the US Department of Health and Human Services (HHS) (37) does not adequately address potential social disparities in exposure, vaccination, or treatment; the possible effects of such disparities; or strategies for minimizing or eliminating them. The HHS plan (37), the federal guidance on vaccine allocation (38), and the recent Centers for Disease Control and Prevention (CDC) guidelines for community-level mitigation strategies (18) should be credited for calling for community engagement and inclusion of a wide variety of stakeholders in planning at the local level. Outreach to providers, community leaders, and organizations, particularly in disadvantaged communities, will be an important component of any strategy for addressing disparities during a pandemic. However, the available versions of official plans do not call attention to the need for special efforts to overcome the greater barriers likely to be faced by socially disadvantaged groups.

On a US government website for pandemic influenza (www.pandemicflu.gov), a question asks which groups would be especially vulnerable during an influenza pandemic. The answer notes that people may be vulnerable for a variety of reasons, including limited access to healthcare; limited proficiency in English; or being disabled, homeless, economically disadvantaged, or a single parent. The response calls for faith-based and community-based organizations to develop plans “to care for dependent populations” and to “provide financial aid to the poor who are unable to work and are in need of emergency income for housing, medicine, or other essential needs” (www.pandemicflu.gov/faq/pandemicinfluenza/pi-0001.html), which implies that attention to the needs of economically or socially vulnerable persons is not primarily a public-sector responsibility but is more a matter for private charity. The 2005 HHS plan (37) itself acknowledges that some groups may need financial assistance if they are unable to work but does not indicate how that assistance would be provided or who would provide it.

Those who are still formulating plans should consider likely differences in influenza exposure and identify potential strategies for mitigating such disparities. Mathematical models have demonstrated that community-based interventions, such as quarantine and individual isolation, may be important for reducing influenza attack rates and overall incidence (29). Most pandemic plans call for limiting public gatherings and closing schools to slow the spread of influenza, without adequately taking into account how implementing these strategies could differentially affect disadvantaged groups. Recent recommendations from CDC go further in recognizing the differential effect of social-distancing measures on vulnerable communities (18). Although CDC advocates flexible work arrangements, income replacement, and job security to minimize the negative effects of social-distancing measures, it pays inadequate attention to those whose jobs will not accommodate these interventions. More specific solutions should be outlined in pandemic preparedness plans to address the economic effects of quarantine on low-income persons, who by staying home may be at risk wage loss, job termination, or both. Job security and income replacement are key components to limiting the effects of potential quarantine measures on disadvantaged persons (39) and should be extended to all persons, regardless of their type of work.

Important decisions also will need to be made concerning access to vaccination and treatment in the event of a pandemic. The federal government’s Draft Guidance on Allocating and Targeting Pandemic Influenza Vaccine (38) provides a basic framework for allocating vaccine during the pandemic. An appendix to that document mentions (on p.17) that the principles of “fairness and equity (recognizing that all persons have equal value, and providing equal opportunity for vaccination among all persons in a priority group)” were considered when drafting the guidelines. Although the proposed schema very reasonably first defines groups of different priority levels according to occupation and then, within the general population, according to age and pregnancy status, it does not provide explicit attention to groups who are vulnerable because of social disadvantage. Nor does it note the need for explicit attention to vulnerable social subgroups, for example, low-wage workers in prioritized occupational fields and low-income and minority pregnant women, infants, and toddlers. We are not questioning the rationality of defining major priority groups according to occupation or of using biological criteria to further prioritize within the general population. Rather, our concern is with the absence of attention to both biological and social risk factors, which must be addressed to overcome the many social barriers to equal opportunity for vaccination.

Well-documented evidence of existing healthcare disparities suggests that during a pandemic shortages of influenza vaccine, antiviral drugs, inpatient services, and healthcare staff will disproportionately affect persons in socially disadvantaged groups. To limit the crowds that might occur at hospitals and clinics, plans for the release of stockpiles of vaccines, medications, or both could include distribution from private pharmacies or doctors’ offices. However, because private pharmacies and private practitioners are less likely to be located in lower income neighborhoods, plans to make access to potentially lifesaving vaccines and drugs speedier and more equitable might, in fact, exacerbate disparities. Distribution plans may need to include mobile community health centers (staffed by nurses and nurse practitioners) that can travel to low-income areas, along with a variety of community medical and other service providers and nontraditional sites like soup kitchens, sheltered workshops, and transit points, which have become popular places for administering yearly influenza vaccine (40). Other factors, such as the availability of transportation to a hospital, might also become more important during a pandemic. Access to a private car may be a major determinant of who is able to obtain care, presenting constraints like those that led to disparities in evacuation from New Orleans before Hurricane Katrina. To ensure that disadvantaged communities are reached and that resources are equitably allocated during an influenza pandemic, preparedness plans can and should involve community-based providers and organizations that are familiar with vulnerable groups.

Social group disparities in exposure, susceptibility, and access to timely and effective treatment for a variety of diseases have been well documented in the United States. Influenza pandemic preparedness plans that fail to explicitly provide guidelines on how to mitigate these issues could lead to decisions that may, on the surface, seem reasonable, but that are likely to exacerbate social group disparities in health outcomes. Given the existence of major disparities in health and healthcare, we cannot expect pandemic preparedness and response planning to eliminate the deep divides that exist between socioeconomic and racial/ethnic groups. These disparities can, however, be minimized through careful planning that considers and proactively addresses vulnerability at each level: exposure to disease, susceptibility to disease if exposed, and treatment of disease. Public officials should systematically consider the additional barriers faced by socially disadvantaged groups at each of these levels and then actively seek ways to address those barriers. Local service providers, leaders of community-based organizations and other organizations working with socially vulnerable groups, and leaders of labor unions representing low-wage service workers are likely to have valuable insights and should be included in the planning process. Plans calling for stakeholder involvement without explicitly emphasizing the need to involve representatives of socially disadvantaged groups are unlikely to be effective at minimizing social disparities during an influenza pandemic.

We have focused here on the United States, but similar fundamental principles—the need for systematic and concrete planning to minimize the social disparities that can be expected to occur in the face of natural disasters such as an influenza pandemic—apply worldwide. Countries with universal financial access to healthcare and strong social safety nets will be best positioned to minimize such disparities. Countries in which large proportions of the population are impoverished or otherwise socially excluded and countries that have more limited resources and weaker public health and social welfare infrastructures will face the greatest challenges. The framework used here—considering and proactively addressing social vulnerability in exposure to pathogens, susceptibility to disease once exposed, and consequences of illness—should be applicable across national and subnational settings.