(A)H1N1 Influenza:
Science and policy collide on defining a 'pandemic'
15 Apr 2009 in Regulatory Science, Regulatory Policy, Information Quality
On June 11 the World Health Organization decreed that the recent outbreak of (A)H1N1 influenza ("swine flue") qualified as a "pandemic." According to reporters for the Washington Post, WHO delayed making this decision long after it technically met its established definition. The reason for delay is that policy officials no longer liked the definition and were concerned that a declaration of a pandemic could lead to panic.
Post staff writer David Brown reports that the decision was "expected for weeks but made with some reluctance" because Phase 6 was supposed to be reserved for viral outbreaks of worldwide scope and illness severity. At a population level, the (A)H1N1 outbreak has not had severe consequences:
Worldwide, 28,774 cases in 74 countries, and 144 deaths, had been reported as of yesterday.
The WHO definition is supposed to be scientific but it is highly subject to subjective judgment that is neither transparent nor reproducible. For that reason, it cannot be discerned whether judgments are largely scientific inferences or reflect the policy preferences of those empowered to exercise judgment. The definition includes "severity of illness" as a factor in deciding which phase to declare, but because it arises relatively early in an outbreak (at the cusp of Phase 3) it provided little help to WHO decision-makers deciding if to declare a Phase 6 pandemic. Yet there seems to be no question that the (A)H1N1 outbreak long ago met the definition for Phase 6:
The move to Phase 6, the highest level in the WHO's graduated scale of pandemic alerts, means the virus is being passed freely between people without easily traced chains of infection -- a state known as "community level transmission" -- in two or more regions of the world.
The line between science (estimating the likely scope, scale and consequences of the outbreak) and policy (what to do about it) appears to be thoroughly muddled. Experts in infectious disease seem to be unable to disentangle scientific facts and inferences from their personal policy preferences:
"I think it was the right call," said Michael T. Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, who has urged pandemic preparedness over the last five years. "We are all sitting here with bated breath, waiting to see what is going to happen in the next six to 12 months."
The dean of U.S. influenza researchers, Edwin D. Kilbourne, 88, agreed. "Even if it errs on the side of being a little bit excessive, the warning should go out that things could get worse," he said.
The line between science and policy appears to have become further muddled insofar as some policy officials may have interfered in the collection of data needed to inform the decision:
A 40-year-old Spanish pediatrician told The Washington Post that soon after the American outbreak began, rapid-test kits for influenza A -- an initial screening tool for finding the new virus -- were removed from the hospital in the Madrid suburbs where he works. Patients who met the "epidemiological criteria" were referred to a central location for testing.
The net effect was to reduce the chance of finding cases in people without travel histories and to prevent early discovery of "community transmission" of the virus.
The reason for this strategy is uncertain, but some observers think that no country wanted to be seen as responsible for triggering the Phase 6 declaration. Chan yesterday named no country's outbreak as the reason for the WHO's decision.
World Health Organization Definitions for Phases of Infectious Disease Pandemic (p. 2)
Phase 1. No new influenza virus subtypes have been detected in humans. An influenza virus subtype that has caused human infection may be present in animals. If present in animals, the risk of human infection or disease is considered to be low.
Phase 2. No new influenza virus subtypes have been detected in humans. However, a circulating animal influenza virus subtype poses a substantial riska of human disease.
Phase 3. Human infection(s) with a new subtype, but no human-to-human spread, or at most rare instances of spreading to a close contact.b
Phase 4. Small cluster(s) with limited human-to-human transmission but spreading is highly localized, suggesting that the virus is not well adapted to humans.b
Phase 5. Larger cluster(s) but human-to-human spreading still localized, suggesting that the virus is becoming increasingly better adapted to humans, but may not yet be fully transmissible (substantial pandemic risk).b
Phase 6. Pandemic increased and sustained transmission in general population.b
a The distinction between phase 1 and phase 2 is based on the risk of human infection or disease resulting from circulating strains in animals. The distinction is based on various factors and their relative importance according to current scientific knowledge. Factors may include pathogenicity in animals and humans, occurrence in domesticated animals and livestock or only in wildlife, whether the virus is enzootic or epizootic, geographically localized or widespread, and/or other scientific parameters.
b The distinction between phase 3, phase 4 and phase 5 is based on an assessment of the risk of a pandemic. Various factors and their relative importance according to current scientific knowledge may be considered. Factors may include rate of transmission, geographical location and spread, severity of illness, presence of genes from human strains (if derived from an animal strain), and/or other scientific parameters.
