CDC Rates Flu Pandemics on Killing Power, with Category Five the Worst

ATLANTA, Feb. 1 -- Much like the power of hurricanes, future influenza pandemics will be rated on a demonstrated case fatality rate as they spread to shore, with a scale of increasingly drastic recommended defenses, the CDC said today.

The CDC said in a 108-page guidance that the non-pharmaceutical response to a pandemic will be linked to a new Pandemic Severity Index, and the response could include such measures as isolation or closing schools for months.

On the basis of the rate of lethality seen elsewhere as the virus spreads, rather than the wind strength of hurricanes, the index will rates pandemics on a scale of increasing severity from one through five.

On the scale, the CDC said, a pandemic with a case fatality rate elsewhere of less than 0.1% would take the lives of no more than 90,000 Americans and would be classed as category one.

On the other hand, a pandemic would be category five if the case fatality rate were greater than 2%. A category five pandemic would be expected to kill more than 1.8 million in the U.S.

While only mass vaccination would be expected to halt a pandemic, multiple partly effective non-drug interventions could slow its spread and reduce mortality and morbidity, the CDC said.

Among them are:

• Isolation and treatment of people with confirmed or probable pandemic flu. The isolation could be at home or in a health-care facility, depending on availability.
• Voluntary home quarantine for members of households with confirmed or probable influenza. Officials should consider prophylactic use of antiviral medications, if possible.
• Closing of schools and child-care programs, coupled with programs to reduce out-of-school social contacts and community mixing.
• Social distancing measures to reduce contact between adults in the community and workplace. This could include cancellation of public gatherings and alteration of work environments and schedules to reduce face-to-face contact.

"The most controversial elements (such as prolonged dismissal of students from schools and closure of childcare programs) are not likely to be needed in less severe pandemics," the CDC said, "but these steps may save lives during severe pandemics."

For instance, the only measure recommended for a category one pandemic would be isolation and treatment of affected people, although local authorities could tailor the response by adding other measures depending on the local situation.

By contrast, a category four or five pandemic would call for the use of all possible measures and communities should expect schools to be closed and public gatherings to be cancelled for up to 12 weeks.

The CDC guidance added that "all such community-based strategies should be used in combination with individual infection control measures, such as hand washing and cough etiquette."

Before a pandemic, the CDC said, local and regional officials should use the Pandemic Severity Index to guide public health planning. Once a pandemic had begun, they would tailor their response according to the level of threat.

The agency said the more research is needed to understand how the various interventions would play out in the event of a pandemic, especially what it called "cascading second- and third-order consequences."

For example, the agency said, closing schools might trigger a wave of worker absenteeism in order to mind children - a consequence that would also have to figure into any planning.

The CDC guidance included six planning guides to mitigate consequences to employers and workers, schools, colleges and universities, childcare programs, faith-based and community organizations, and individuals and families.

Communities will need to be especially vigilant about the effect of pandemic measures on vulnerable people, including the poor, homeless, elderly, or institutionalized, the CDC said.

"While the challenge is formidable, the consequences of facing a severe pandemic unprepared will be intolerable," the agency concluded.