Influenza causes seasonal epidemics of disease resulting in an average of 14.8 deaths per 100 000 or 600 deaths in Singapore each year (USA-19.6, Hong Kong-16.4). A pandemic occurs when there is a major change in the influenza virus such that most or all of the world’s population has never been exposed previously and is thus vulnerable to the virus. An influenza pandemic has a greater potential to cause rapid increases in death and illnesses than virtually any other natural health threat.

In Jan 04, health authorities in Vietnam and Thailand reported their first human cases of infection with avian influenza caused by an H5N1 strain. The cases in humans are directly linked to outbreaks of highly pathogenic H5N1 avian influenza in poultry initially reported in Korea in mid-December 2003 and subsequently confirmed in an additional seven Asian countries (Vietnam, Japan, Thailand, Cambodia, China, Laos and Indonesia). As at end 04, no country other than Vietnam and Thailand had reported human cases. In Sep 04, Thailand reported a probable case of inefficient human-to-human transmission in a family cluster. A resurgence of poultry outbreaks and human cases has also been reported in Vietnam since December 2004. In February 2005, Cambodia reported its first human case of avian influenza. As of April 05, there have been 89 reported human cases resulting in 52 deaths. Based on these figures, the fatality rate is 60% with Vietnam and Cambodia continuing to report new cases.

The World Health Organization (WHO), in a report released at its 115th Executive Board Meeting on 20 Jan 05, expressed concern over the possibility of the avian influenza in Asia evolving into an influenza pandemic. WHO highlighted that the events in 2004, supported by epidemiological and virological surveillance, have given the world an unprecedented warning that a pandemic may be imminent. WHO warned that although the changing nature of influenza viruses prevented precise predictions of the occurrence of pandemics, the conditions favouring the emergence of a pandemic had been met save one: efficient human-to-human transmission. Hence, WHO urged all countries to undertake or intensify preparedness activities as a matter of urgency.