The classical definition of a pandemic is not elusive

Bull World Health Organ 2011;89:539–540 | doi:10.2471/BLT.11.089086540 Round table Definition of pandemic influenza Discussion gets and grants is fierce. The pharmaceutical industry and the media only reacted to this welcome boon. We therefore need fewer, not more “pandemic preparedness” plans or definitions. Vertical influenza planning in the face of speculative catas- trophes is a recipe for repeated waste of resources and health scares, induced by influenza experts with vested interests in exaggeration. There is no reason for expecting any upcoming pandemic to be worse than the mild ones of 1957 or 1968,7 no reason for striking pre-emptively, no reason for believing that a proportional and balanced response would risk lives. The opposite of pre-emptive strikes against worst-case scenarios are adaptive strategies that respond to emerging diseases of any nature based on the evidence of observed virulence and the effectiveness of control measures. This requires more generic capacity for disease surveillance, prob- lem identification, risk assessment, risk communication and health-care response.1 Such strengthened general capacity can respond to all health emergencies, not just influenza. Resources are scarce and need to be allocated to many com- peting priorities. Scientific advice on resource allocation is best handled by generalists with a comprehensive view on health. Disease experts wish to capture public attention and sway resource allocation decisions in favour of the disease of their interest. We referred previously to the principles of guidance on health by the British National Institute for Health and Clinical Excellence (NICE),2 cited as “We make independent decisions in an open, transparent way, based on the best available evidence and including input from experts and interested parties.”8 Support from disease experts is cru- cial in delivering opinion, scholarly advice and evidence to a team of independent general scientists. But this team should independently propose decisions to policy-makers and be held accountable for them. The key to responsible policy-making is not bureaucracy but accountability and independence from interest groups. Decisions must be based on adaptive responses to emerg- ing problems, not on definitions. WHO should learn to be NICE: accountable for reasonableness in a process of open- ness, transparency and dialogue with all the stakeholders, and particularly the public.9 ■ Competing interests: None declared. References 1. Bonneux L, Van Damme W. An iatrogenic pandemic of panic. BMJ 2006;332:786–8. doi:10.1136/bmj.332.7544.786 PMID:16575086 2. Bonneux L, Van Damme W. Preventing iatrogenic pandemics of panic. Do it in a NICE way. BMJ 2010;340(jun09 3):c3065. doi:10.1136/bmj.c3065 PMID:20534667 3. Füredi F. Culture of fear: risk-taking and the morality of low expectation. New York: Continuum; 2002. 4. Jefferson T, Di Pietrantonj C, Rivetti A, Bawazeer GA, Al-Ansary LA, Ferroni E. Vaccines for preventing influenza in healthy adults. Cochrane Database Syst Rev 2010;7:CD001269. PMID:20614424 5. Jefferson T, Jones M, Doshi P, Del Mar C, Dooley L, Foxlee R. Neuraminidase inhibitors for preventing and treating influenza in healthy adults. Cochrane Database Syst Rev 2010;2:CD001265. PMID:20166059 6. Cohen D, Carter P. WHO and the pandemic flu “conspiracies”. BMJ 2010;340:c2912. doi:10.1136/bmj.c2912 PMID:20525679 7. Morens DM, Taubenberger JK. Understanding influenza backward. JAMA 2009;302:679–80. doi:10.1001/jama.2009.1127 PMID:19671909 8. National Institute for Health and Clinical Excellence [Internet]. London: NICE; 2011. Available from: http://www.nice.org.uk/ [accessed 14 April 2011]. 9. Daniels N. Accountability for reasonableness. BMJ 2000;321:1300–1. doi:10.1136/bmj.321.7272.1300 PMID:11090498 The classical definition of a pandemic is not elusive Heath Kellya Doshi argues cogently that the definition of pandemic influ- enza in 2009 was elusive but does not refer to the classical epidemiological definition of a pandemic.1 A pandemic is defined as “an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually af- fecting a large number of people”.2 The classical definition includes nothing about population immunity, virology or disease severity. By this definition, pandemics can be said to occur annually in each of the temperate southern and northern hemispheres, given that seasonal epidemics cross international boundaries and affect a large number of people. However, seasonal epidemics are not considered pandemics. A true influenza pandemic occurs when almost simul- taneous transmission takes place worldwide. In the case of pandemic influenza A(H1N1), widespread transmission was documented in both hemispheres between April and Septem- ber 2009. Transmission occurred early in the influenza season in the temperate southern hemisphere but out of season in the northern hemisphere. This out-of-season transmission is what characterizes an influenza pandemic, as distinct from a pandemic due to another type of virus. Simultaneous worldwide transmission of influenza is suf- ficient to define an influenza pandemic and is consistent with the classical definition of “an epidemic occurring worldwide”. There is then ample opportunity to further describe the poten- tial range of influenza pandemics in terms of transmissibility and disease severity. The emerging evidence for A(H1N1) is that transmissibility, as estimated by the effective reproduc- tion number (R, or average number of people infected by a single infectious person) ranged from 1.2 to 1.3 for the general population but was around 1.5 in children (Kathryn Glass, Australian National University, personal communication). Some early estimates of R for pandemic influenza H1N1 2009 may have been overestimated.3 Severity, as estimated by the case fatality ratio, probably ranged from 0.01 to 0.03%.4–6 These values are very similar to those normally seen in the case of seasonal influenza.7,8 However, the number of deaths was higher in younger people, a recognized feature of previous influenza pandemics.9 It is tempting to surmise that the complicated pandemic definitions used by the World Health Organization (WHO) and the Centers for Disease Control and Prevention of the United States of America involved severity1,10 in a deliberate attempt to garner political attention and financial support for pandemic preparedness. As noted by Doshi, the perceived a Victorian Infectious Diseases Reference Laboratory, Department of Epidemiology, Locked Bag 815, Carlton South, Vic. 3053, Australia (e-mail: heath.kelly@mh.org.au). Bull World Health Organ 2011;89:540–541 | doi:10.2471/BLT.11.088815 541 Round table Definition of pandemic influenzaDiscussion need for this support can be understood given concerns about influenza A(H5N1) and the severe acute respiratory syndrome (SARS). However, conflating spread and sever- ity allowed the suggestion that 2009 A(H1N1) was not a pandemic. It was, in fact, a classical pandemic, only much less severe than many had anticipated or were prepared to acknowledge, even as the evidence accumulated. In 2009 WHO declared a pandemic several weeks after the criteria for the definition of a classical pandemic had been met. Part of the delay was no doubt related to the nexus between the formal declaration of a pandemic and the manufacture of a pandemic-specific vaccine. If a classical pandemic definition had been used, linking the declaration to vaccine production would have been unnecessary. This could have been done with a severity index and, depending on the availability and quality of the emerging evidence on severity, a pandemic specific vaccine may have been deemed unnecessary. Alternatively authorities may have decided to order vaccine in much smaller quantities. The response to A(H1N1) has been justified as being precautionary, but a precautionary response should be ratio- nal and proportionate and should have reasonable chances of success. We have argued that the population-based public health responses in Australia and, by implication, elsewhere, were not likely to succeed.11 Similarly, the authors of the draft report on the response to the International Health Regula- tions during the 2009 pandemic note that what happened during the pandemic reflected the activity of the virus and, by implication, not the interventions.10 Risk is assessed by anticipation of severity and precaution should be calibrated to risk. As Doshi has argued, we need to redefine pandemic influenza. We can then describe the potential severity range of future pandemics. Finally, we need to use evidence to assess severity early to anticipate risk. ■ Competing interests: None declared. References 1. Doshi P. The elusive definition of pandemic influenza. Bull World Health Org 2011;89:532–538. 2. Last JM, editor. A dictionary of epidemiology, 4th edition. New York: Oxford University Press; 2001. 3. Mercer G, Glass K, Beckers N. Effective reproduction numbers are commonly overestimated early in a disease outbreak. Stat Med 2011;30:984–94. 4. Donaldson LJ, Rutter PD, Ellis BM, Greaves FE, Mytton OT, Pebody RG et al. Mortality from pandemic A/H1N1 2009 influenza in England: public health surveillance study. BMJ 2009;339:b5213. doi:10.1136/bmj.b5213 PMID:20007665 5. Bandaranayake D, Huang QS, Bissielo A, Wood T, Mackereth G, Baker MG et al.; 2009 H1N1 Serosurvey Investigation Team. Risk factors and immunity in a nationally representative population following the 2009 influenza A(H1N1) pandemic. PLoS ONE 2010;5:e13211. doi:10.1371/journal.pone.0013211 PMID:20976224 6. McVernon J, Laurie K, Nolan T, Owen R, Irving D, Capper H et al. Seroprevalence of 2009 pandemic influenza A(H1N1) virus in Australian blood donors, October - December 2009. Euro Surveill 2010;15:pii=19678. PMID:20946757 7. Viboud C, Tam T, Fleming D, Handel A, Miller MA, Simonsen L. Transmissibility and mortality impact of epidemic and pandemic influenza, with emphasis on the unusually deadly 1951 epidemic. Vaccine 2006;24:6701–7. doi:10.1016/j.vaccine.2006.05.067 PMID:16806596 8. Wilson N, Baker MG. The emerging influenza pandemic: estimating the case fatality ratio. Euro Surveill 2009;14:pii=19255. PMID:19573509 9. Miller MA, Viboud C, Balinska M, Simonsen L. The signature features of influenza pandemics–implications for policy. N Engl J Med 2009;360:2595– 8. doi:10.1056/NEJMp0903906 PMID:19423872 10. Report of the review committee on the functioning of the International Health Regulations (2005) and on pandemic influenza A (H1N1). International Health Regulations Review Committee; 2009. Available from: http://www.who.int/ ihr/preview_report_review_committee_mar2011_en.pdf [accessed 13 April 2011]. 11. Kelly HA, Priest PC, Mercer GN, Dowse GK. We should not be complacent about our population-based public health response to the first influenza pandemic of the 21st century. BMC Public Health 2011;11:78. doi:10.1186/1471-2458-11-78 PMID:21291568 Living forwards, understanding backwards Nicholas F Phina It has been said that pandemics are lived forwards and un- derstood backwards. The 2009 influenza pandemic is no exception. The identification of the new influenza virus strain in the United States of America coincided with many media reports describing a very severe pneumonia affecting young Mexican adults – echoes of 1918! Hard data were sparse and quoted case fatality rates ranged from 0.3% to 2.5% of confirmed cases as late as September 2009. With the benefit of hindsight it is easy to say that the disease caused by the virus was in fact mild for most people and that this action or that action should have been taken. However, in real time with little reliable data on the effects of the virus on individuals and communities and faced with the need to make time-critical decisions, sovereign nations across the world responded differently. It is important to remember that the World Health Organization (WHO) remit is to help governments determine the level of interventions required as part of their response to threats to international health. Unfortunately, the fact that WHO issued revised pan- demic guidance just as the pandemic was starting generated confusion. Under the new guidance,1 pandemic phases 4 to 6 differed significantly from the 2005 guideline document,2 and this made communication difficult. Individuals have made great play of the change to the wording of one sentence that was part of a 60-page docu- ment before phase 6 (the so-called start of the pandemic) was declared. In fact, in several places the WHO 2009 guidance document describes phases 5 to 6 as the pandemic period and clearly states that “during phases 5–6 (pandemic) ac- tions shift from preparedness to response at a global level.” From this it can be argued that the pandemic was actually declared on 29 April 2009, five days before the quoted change in definition. a Health Protection Services, 61 Colindale Avenue, London, NW9 5EQ, England (e-mail: nick.phin@hpa.org.uk).