Living forwards, understanding backwards



Nicholas F Phin

Health Protection Services, 61 Colindale Avenue, London, NW9 5EQ, England (e-mail:



It has been said that pandemics are lived forwards and understood 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 pandemic 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 document 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) actions 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.

In the United Kingdom of Great Britain and Northern Ireland, a new national influenza pandemic strategy was published for consultation on 22 March 2011.3 This has taken on board many of the lessons learned during the 2009 pandemic. However, the strategy still recognizes the need for an initially precautionary approach, given the speed with which the virus can spread and the paucity of data that will be available at the start of a pandemic, although it states that proportionality and flexibility should guide the response as information about the virus and its effects become available. The strategy is now better adapted to the needs of the United Kingdom and is proposing a new phased response that is not linked to the WHO phases. This reflects the fact that in the United Kingdom the first cases were detected in late April 2009 and that using the WHO phases, which are global indicators of spread, proved to be unhelpful.

Peter Doshi highlights the lack of a definition of a pandemic.4 There is also no definition of a pandemic wave or severity, both key issues when it comes to describing the progress and impact of a pandemic. I don't believe this reflects a lack of willingness to formulate such definitions, but rather, a lack of international consensus stemming from the absence of key data and the recognition that severity, impact and other descriptors can only be applied with certainty historically.

Competing interests: None declared.



1. Pandemic influenza preparedness and response. Geneva: World Health Organization; 2009. Available from: [accessed 20 April 2011]          .

2. WHO global influenza preparedness plan. Geneva: World Health Organization; 2005. Available from: [accessed 20 April 2011]          .

3. UK influenza pandemic preparedness strategy 2011: strategy for consultation [Internet]. London: Department of Health; 2011. Available from: [accessed 20 April 2011]          .

4. Doshi P. The elusive definition of pandemic influenza. Bull World Health Organ 2011;89:532–8.         

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