Symposium on Pandemic Influenza - October 2007
By Elizabeth Graves Love, MPH; Kelly N. Reed-Hirsch, MPH, CHES; and Lucinda J. Kilborn, MPH
Current avian influenza activity in Asia and Europe underscores the importance of planning for pandemic influenza in the United States. In response, health officials at the federal, state, and local levels have accelerated their efforts to coordinate planning to prepare and respond to pandemic influenza. Three overarching goals drive the planning efforts:
- To prevent and/or minimize morbidity and mortality through limiting the spread of disease,
- To minimize social disruption, and
- To minimize economic effects. 1
The primary strategies for combating pandemic influenza include vaccination, antiviral medications, and nonpharmaceutical interventions (NPIs), also known as community mitigation strategies. 1 Vaccination would be the single most effective intervention, but having available a vaccine that is well-matched against the circulating virus strain when a pandemic begins is unlikely. Current technology would require four to six months for vaccine development of a new antigenic strain, and, once developed, production capacity would limit the availability of vaccines. 1
Antiviral medications could be used for both treatment and prophylaxis, but the effectiveness of current antivirals against a future pandemic strain is unknown, both in terms of efficacy and potential for resistance, and current quantities are limited. 2 These realities emphasize the importance of NPIs as a critical countermeasure against pandemic influenza.
Two approaches to applying NPIs exist. The first is to apply measures that decrease the probability that contact between uninfected and infected individuals will result in disease transmission. Examples of such measures include consistently employing cough etiquette and hand-hygiene techniques, the use of personal protective equipment, and infection-control protocols. The second approach is to apply measures that decrease opportunities for contact between infected and uninfected individuals. Examples include isolation, quarantine, travel advisories, cancellation of mass gatherings, school closures, and certain social distancing techniques.
The intent of the application of NPIs at the outset of a pandemic would be to reduce the total number of cases in a community, thus reducing overall morbidity and mortality and allowing time for the production and distribution of vaccines and antiviral medications. 1 Fig. 1 illustrates the intended effect of NPIs following a pandemic outbreak within a community compared with no intervention. In short, NPIs have the potential to delay, compress, and diminish the outbreak peak.
The potential effectiveness of NPIs during a pandemic has been studied by historical analysis and mathematical modeling. A number of recent studies examined the effectiveness of NPIs applied in the United States during past pandemics, with a focus on the severe 1918 Spanish flu pandemic. In general, these analyses compare the pandemic severity of cities that implemented NPIs with those that did not. Together, these studies indicate that cities with early, sustained NPI implementation experienced a delayed and flattened epidemic peak, compared with cities that did not implement NPIs or that implemented them later in the course of the outbreak. 3
A study by Hatchett et al observed 19 NPI interventions in 17 U.S. cities during the 1918 pandemic and found that early multiple NPIs were associated with reduced disease transmission. 4 Further, cities that enacted NPIs early and kept them in place throughout the pandemic saw death rates approximately 50 percent lower than those cities that did not enact such measures.
Certain NPIs, including school closures and suspension of mass gatherings such as those in church services and in theaters, were associated with lower peak death rates as well. However, the authors concluded that no single intervention was associated with improved aggregate outcomes. 4
The utility of such historical analyses has limitations, such as the relevance of comparing early 20th century societal, health, and medical conditions with those of the 21st century. To complement historical analyses, mathematical modeling methods have been applied to determine the potential effectiveness of NPIs during a pandemic in conditions mirroring 21st century United States. A recent report from the Institute of Medicine summarized available epidemic models for community containment strategies and concluded that targeted layered containment using NPIs would reduce influenza transmission and attack rates, even with modest community compliance. Early isolation of ill persons and school closures were the most effective interventions observed. 3
A recent guidance document released by the U.S. Centers for Disease Control and Prevention (CDC) proposes a framework for community mitigation based on implementing a targeted layered containment strategy using NPIs at the outset of a pandemic. The framework includes the following four interventions:
- Isolation and antiviral treatment (as appropriate and available) of individuals with confirmed or probable cases of illness with the pandemic strain of influenza. Depending on illness severity and capacity of the health care system, a person could be isolated in his or her home or in a health care setting.
- Voluntary home quarantine of household contacts of persons with confirmed or probable illness with a pandemic strain of influenza. If available in sufficient supply, prophylactic use of antivirals could be considered for these individuals.
- School closures, including public and private schools, colleges, universities, and child day care programs. Social distancing measures should be implemented, as well as school closures, to reduce out-of-school contact among children.
- Social distancing measures aimed at reducing contact among adults in the community and in the workplace. Examples include canceling mass gatherings and instituting workplace policies that decrease social density, such as telecommuting and leave policies that promote adherence with NPIs. 1
The guidance document also highlights the importance of individual infection-control practices such as hand hygiene and cough etiquette. Also, the Pandemic Severity Index is proposed as a method to assist localities with decision making regarding the implementation of NPIs. This index classifies pandemics into five categories: Category 1 is the least severe (comparable to seasonal influenza) and Category 5 is the most severe (comparable to the 1918 pandemic) ( Fig. 2 ).
Specific examples for NPIs for each category are also proposed. For example, voluntary home isolation of ill persons is recommended for a Category 1 pandemic, while school closures and social distancing measures are not. School closures for at least 12 weeks are recommended for Category 4 and 5 pandemics, and school closures should be considered for approximately four weeks during a Category 2 or 3 pandemic. For all categories, the guidance recommends that the "trigger point" for initiating an intervention should be the arrival and transmission of pandemic influenza virus in a community. 1
When considering implementing NPIs, the potential health benefits must be weighed against their potential burdens to society. For example, the success of school closures hinges upon the availability of adults to care for children at home - in many instances, this would place financial burden upon adults who must take leave from work to care for children. Therefore, it is crucial that appropriate NPIs are applied at the appropriate time during a pandemic; the least restrictive measure that provides public health benefit is the preferred intervention.
In Texas, decision making regarding NPIs during a pandemic ultimately rests at the local level, with a key decision maker being the local health authority. Appointed by the state, local health authorities are licensed physicians charged with administering laws related to public health within their jurisdiction. In accordance with the Texas Health and Safety Code, these laws include those related to community disease control measures such as isolation and quarantine. 5
Texas has 172 local health authorities, many affiliated with local health departments. 6 During a pandemic, local health officials, including health authorities, will work with community stakeholders and state partners to review epidemiological data, weigh potential health benefits with potential societal and economic burdens, and apply the appropriate NPIs. Supported by federal funds intended to enhance local preparedness for pandemic influenza, public health officials throughout Texas are currently developing plans that address the implementation of NPIs within their communities.
Physicians will likely be among the first to diagnose and treat pandemic influenza within their communities. Many individuals will look to their physicians for information and guidance about the pandemic situation and recommendations enacted by local health officials. Physicians must therefore remain informed about local plans for responding to pandemic influenza, particularly plans for enacting community control measures such as vaccines, antivirals, and NPIs. Armed with this information, physicians can engage patients in following recommendations that can protect their families' health and well-being during a pandemic.
Elizabeth Love, Kelly Reed-Hirsch, and Lucinda Kilborn are with Harris County Public Health and Environmental Services. Ms. Love is the chief of the Office of Policy and Planning, Ms. Reed-Hirsch is the public health program manager for school health and injury prevention, and Ms. Kilborn is chief epidemiologist.
Fig. 1. The intended effect of nonpharmaceutical interventions following a pandemic outbreak within a community compared with no intervention.
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Fig. 2. Pandemic Severity Index.
Source for figures: Interim Pre-pandemic Planning Guidance: Community Strategy for Pandemic Influenza Mitigation in the United States - Early, Targeted, Layered Use of Nonpharmaceutical Interventions. Centers for Disease Control and Prevention; February 2007. http://www.pandemicflu.gov/plan/community/community_mitigation.pdf .
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- U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Interim Pre-Pandemic Planning Guidance: Community Strategy for Pandemic Influenza Mitigation in the United States; 2007. http://www.pandemicflu.gov/plan/community/community_mitigation.pdf . Accessed July 5, 2007.
- Hayden FG. Antiviral resistance in influenza viruses: implications for management and pandemic response. N Engl J Med . 2006;354(8):785-788.
- Institute of Medicine; Committee on Modeling Community Containment for Pandemic Influenza. Modeling Community Containment for Pandemic Influenza. A Letter Report. Washington, D.C.: The National Academies Press; 2006.
- Hatchett RJ, Mecher CE, Lipsitch M. Public health interventions and epidemic intensity during the 1918 pandemic. Proc Natl Acad Sci U S A . 2007;104(18):7582-7587.
- Texas Health and Safety Code §81 and §121.
- Texas Health and Human Services Commission. An overview of the Department of State Health Services. http://www.dshs.state.tx.us/orgchart/dshsbriefing.pdf . Accessed July 9, 2007.
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