The elusive definition of pandemic influenza

– by Peter Doshi –

In 2009, governments throughout the world mounted large and costly responses to the H1N1 influenza outbreak. These efforts were largely justified on the premise that H1N1 influenza and seasonal influenza required different management, a premise reinforced by the decision on the part of the World Health Organization (WHO) to label the H1N1 influenza outbreak a “pandemic”. However, the outbreak had far less serious consequences than experts had predicted, a fact that led many to wonder if the public health responses to H1N1 had not been disproportionately aggressive. In addition, concern over ties between WHO advisers and industry fuelled suspicion about the independence and appropriateness of the decisions made at the national and international levels.

Central to this debate has been the question of whether H1N1 influenza should have been labelled a “pandemic” at all. The Council of Europe voiced serious concerns that the declaration of a pandemic became possible only after WHO changed its definition of pandemic influenza. It also expressed misgivings over WHO’s decision to withhold publication of the names of its H1N1 advisory Emergency Committee. WHO, however, denied having changed any definitions and defended the scientific validity of its decisions, citing “numerous safeguards” for handling potential conflicts of interest.

At stake in this debate are the public trust in health officials and our collective capacity to respond effectively to future disease threats. Understanding this controversy entails acknowledging that both parties are partially correct, and to resolve it we must re-evaluate how emerging threats should be defined in a world where the simple act of labelling a disease has enormous social, economic and political implications.

What sparked the controversy

Since 2003, the top of the WHO Pandemic Preparedness homepage has contained the following statement: “An influenza pandemic occurs when a new influenza virus appears against which the human population has no immunity, resulting in several simultaneous epidemics worldwide with enormous numbers of deaths and illness.” However, on 4 May 2009, scarcely one month before the H1N1 pandemic was declared, the web page was altered in response to a query from a CNN reporter. The phrase “enormous numbers of deaths and illness” had been removed and the revised web page simply read as follows: “An influenza pandemic may occur when a new influenza virus appears against which the human population has no immunity.” Months later, the Council of Europe would cite this alteration as evidence that WHO changed its definition of pandemic influenza to enable it to declare a pandemic without having to demonstrate the intensity of the disease caused by the H1N1 virus.

A description versus a definition

Harvey Fineberg, chairman of a WHO-appointed International Health Regulations (IHR) Review Committee that evaluated WHO’s response to H1N1 influenza, identified the definition of pandemic influenza as a “critical element of our review”. In a draft report released in March, the committee faulted WHO for “inadequately dispelling confusion about the definition of a pandemic” and noted WHO’s “reluctance to acknowledge its part in allowing misunderstanding” of the web page alteration, which WHO has characterized as a change in the “description” but not in the “definition” of pandemic influenza. “It’s not a definition, but we recognize that it could be taken as such … It was the fault of ours, confusing descriptions and definitions”, a WHO communications officer declared. Indeed, the Council of Europe was not alone in claiming that the “definition” had been changed.

WHO argues that this phrase – which could be more neutrally referred to as a description–definition – had little bearing on policy responses; a WHO press release states that it was “never part of the formal definition of a pandemic” and was never sent to Member States, but simply appeared in “a document on WHO’s website for some months”. In actuality, the description–definition was displayed at the top of the WHO Pandemic Preparedness home page for over six years and is consistent with the descriptions of pandemic influenza put forth in various WHO policy documents over the years. However, while the original description–definition unambiguously describes disease severity and certainly reflects general assumptions about pandemic influenza before novel H1N1 emerged, it is unrelated to the criteria WHO applied to declare H1N1 influenza a pandemic.

Definitions of pandemic phases, not pandemic influenza

In a press conference, WHO explained that “the formal definitions of pandemics by WHO can be seen in the guidelines”. This was a reference to WHO’s pandemic influenza preparedness guidelines, first developed in 1999 and revised in 2005 and 2009. However, none of these documents contains what might reasonably be considered a formal definition of pandemic influenza, a fact that may explain why WHO has refrained from offering a quotable definition despite its repeated assurances that “the definition” was never changed. The startling and inevitable conclusion is that despite ten years of issuing guidelines for pandemic preparedness, WHO has never formulated a formal definition of pandemic influenza.

Peter Doshi is a senior editor at The BMJ and on the News & Views team. Based in Baltimore, he is also an assistant professor of pharmaceutical health services research at the University of Maryland School of Pharmacy. He received his Ph.D. in history, anthropology, and science, technology and society from the Massachusetts Institute of Technology.

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