Influenza is a familiar infection in the UK, especially during winter. Almost every year new drifted strains of influenza emerge giving rise to morbidity and mortality, mainly in older persons and young children. Pandemic influenza is different: its emergence and potential impact are both difficult to predict.
A pandemic of influenza is the result of a new influenza A virus subtype emerging which is markedly different from recently circulating strains and is able to:
infect people (rather than, or in addition to, animals or birds) spread from person to person, and cause illness in a high proportion of the people infected, and also spread widely, because a high proportion of the population is susceptible (most people will have little or no immunity to the new virus because they will not have been infected or vaccinated with it or a similar virus before).New subtypes of influenza have emerged sporadically over the last century. In 1918 a devastating and unusual pandemic caused by influenza A, subtype H1N1 (Spanish flu ™) killed between 20 and 40 million people worldwide. Other pandemics that followed had a less devastating impact but were nevertheless severe. Influenza A, subtype H2N2 (Asian flu ™) emerged in 1957 and H3N2 (Hong Kong flu ™) in 1968.
The circumstances still exist for a new influenza virus with pandemic potential to emerge and spread and the longest interval so far recorded between pandemics is 39 years. The unpredictability of the timing of the next pandemic is underlined by the occurrence of several large outbreaks of highly pathogenic avian influenza since the early 1980s. Large outbreaks in poultry were described in Pennsylvania in 1982 (A/H5N2), Mexico in 1993 (A/H5N2), Hong Kong in 1997 (A/H5N1), Hong Kong again in 2003 (A/H9N2) and The Netherlands in 2003 (A/7N7). Both the Hong Kong and Netherlands outbreaks were associated with epizootic transmission to humans. However, by far the most serious was the massive and unprecedented outbreak of highly pathogenic influenza (A/H5N1) affecting poultry in East and South East Asia in late 2003 and again in 2004. This outbreak has so far been associated with a small number of human cases and a high proportion of deaths. Whether these outbreaks presage the emergence of an A/H5N1 strain with capacity to spread efficiently between humans is unknown.
Other events and developments that inform the creation of this plan are:
The creation of a new organisation, the Health Protection Agency from the Public Health Laboratory Service, the Centre for Applied Microbiological Research (CAMR), the National Radiological Protection Board, and Consultants in Communicable Disease Control and their Health Protection Teams formerly employed by the NHS. The emergence and successful control of Severe Acute Respiratory Syndrome (SARS) using aggressive infection control methods combined with standard public health interventions. The development and licensing of a new class of drug (neuraminidase inhibitors) active against influenza A and B.Full text version of the HPA Influenza Pandemic Contingency Plan (PDF File)
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