Feds map plans for response to flu pandemic

Mutable virus may eventually outwit experts

Citing the unique ability of influenza virus infections to cause sudden, pervasive infection on a global scale in all age groups, a U.S. government working group is compiling a disaster response plan for the event of a worldwide flu pandemic.

A draft ’conceptual plan” obtained by Hospital Infection Control outlines the basic public health and government response to a sweeping flu pandemic along the lines of the 1918 virus that caused 20 million deaths worldwide.1

’A hallmark of large-scale influenza epidemics and pandemics is their ability to cause major disruption of routine medical services,” the draft states. ’As an epidemic passes through a population, it first leads to an increase in respiratory illnesses, then pneumonias and other infection-related complications, and finally deaths. Each of these events strains the ability of routine community medical services to provide adequate care, especially when providers themselves frequently become infected.”

In an effort to cope with community disruption and increased demand for medical services on a national, virtually simultaneous scale, it is essential that contingency plans for dealing with such emergencies be developed in advance of the pandemic at the national, state, and local levels, the working group recommends. Federal agencies working on the plan with the help of non-government consultants include the Centers for Disease Control and Prevention in Atlanta, and the Bethesda, MD-based Food and Drug Administration and the National Institutes of Health.

Discussed recently at a meeting in Washington, DC, the draft plan treats the emergence of another flu pandemic with a certain inevitability, saying an antigenic shift could occur that would create a highly transmissible, virulent virus that could reach susceptible populations before a vaccine could be produced and distributed. The unusual properties of the influenza virus genome include a rapid rate of evolution, creating ’progressive antigenic drift of the hemagglutinin (HA) and neuraminidase (NA) surface antigens towards new variants,” the draft states.

The cornerstone of flu prevention remains global virologic surveillance, which consists of 110 designated laboratories in 79 countries. The primary purpose of this network is to detect the emergence and spread of new antigenic variants of influenza, which often signal a need to update the formulation of influenza vaccine. Because the effectiveness of the vaccine is determined almost solely by the antigenic relatedness of the vaccine and circulating wild strains, the maintenance of adequate virologic surveillance must be among the highest priorities, the draft plan states.

The changing flu virus is tracked and matched annually in influenza vaccine production, but current production techniques may be inadequate if a new virus emerges for which a large portion of the population would be susceptible. Even under optimum conditions, approximately six to eight months would be needed from the time a new variant is identified until large quantities of vaccine are ready for use, according to the plan.

Epidemic would outpace vaccine production

Although universal vaccination should be the goal in the event of a pandemic, there are no assurances that sufficient doses of vaccine could be available in time. Because of this threat, it is essential that a priority system be developed, with the primary aims of maintaining national security, preventing as many deaths as possible, minimizing morbidity, and minimizing social disruption, the draft recommends. In addition to vaccinating key government officials and people who provide essential community services, priority groups for immunization would be people at high risk for influenza-related mortality and severe morbidity (i.e., the elderly or immunocompromised), medical care providers, infants less than one year old, and pregnant women.

Two other pandemics of influenza have occurred since 1918. However, the number of deaths due to the more recent pandemics in 1957 (’Asian flu”) and 1968 (’Hong Kong flu”) were reduced in part by antibiotic therapy and aggressive supportive care. Still, both pandemics were associated with high rates of morbidity and severe social disruption, with combined economic losses of $32 billion in 1995 dollars. Of no less concern has been the legacy left by these pandemics: the subsequent emergence of annual epidemics of varying severity, with at least 750,000 associated deaths in the United States alone since 1958. Approximately 90% of those deaths have occurred among the elderly and people with chronic underlying medical conditions, who are particularly vulnerable to the effects of influenza infection on the cardiovascular and pulmonary systems. Approximately 150,000 hospitalizations attributable to influenza occur in the United States each year, with associated costs in the range of $1 billion to $3 billion, the draft report estimates.

Reference

1. Federal Working Group on Influenza Pandemic Preparedness. Prevention and Control of Influenza in the United States: Preparing for the Next Pandemic. Draft # 6. January, 1996.