110 Pandemic Preparedness

Chapter 5: Pandemic Preparedness

Gustavo Reyes-Terán and René Gottschalk

Introduction

Previous Influenza Pandemics

Three influenza pandemics (worldwide epidemics) are known to have occurred, all caused by influenza A viruses. When a significant change in at least one of the influenza A virus surface proteins haemagglutinin and neuraminidase occurs spontaneously, nobody has immunity to this entirely new virus. If the virus also achieves efficient human-to-human transmission and has the ability to replicate in humans causing serious illness, a pandemic can occur. This happened in 1918 (the “Spanish flu”, caused by a H1N1 subtype), in 1957 (the “Asian flu” caused by a H2N2 subtype) and in 1968 (the “Hong Kong flu”, caused by a H3N2 subtype). Conservative estimates suggested that the mortality from the 1918 pandemic was 20 to 40 million. However, recent studies from Africa and Asia suggest that the number of victims worldwide might have been closer to 50–100 million (Johnson 2002).

Influenza experts have estimated that in industrialised countries alone, the next influenza pandemic may result in up to 130 million outpatient visits, 2 million hospital admissions and 650,000 deaths over two years. The impact is likely to be even greater in developing countries (WHO 2004). A 1918-type influenza pandemic today is projected to cause 180–360 million deaths globally (Osterholm 2005).

H5N1 Pandemic Threat

So far (January 2006), nine countries in the Far East have reported poultry outbreaks of a highly pathogenic H5N1 avian influenza virus: the Republic of Korea, Vietnam, Japan, Thailand, Cambodia, Laos, Indonesia, China, and Malaysia. The outbreaks in Japan, Malaysia, and the Republic of Korea were successfully controlled, but the virus seems to have become endemic in several of the affected countries. The Southeast Asian outbreaks resulted in the death or destruction of more than 150 million birds and had severe consequences for agriculture, most especially for the many rural farmers who depend on small backyard flocks for income and food.

The recent outbreaks of the same virus strain in birds in Russia, Kazakhstan, Turkey, Romania, and Croatia provide evidence that it has spread beyond the initial focus (WHO 2005a, WHO 2005b).

Human cases of avian influenza A (H5N1), most of which have been linked to direct contact with diseased or dead poultry in rural areas, have been confirmed in six countries: Vietnam, Thailand, Cambodia, Indonesia, China, and Turkey (see Table 1). The figures for confirmed human cases of avian influenza A (H5N1) infection reported to the WHO are regularly updated on the WHO webpage (WHO 2005c).