Pandemic
Disease Information
What is Pandemic Influenza?
Introduction
An influenza pandemic is a global outbreak of disease that occurs when a new influenza virus appears or "re-emerges" in the human population against which the human has no immunity, spreads and causes disease worldwide.
Pandemic influenza emerges as a result of influenza viruses undergoing major genetic changes known as antigenic shift. It is usually associated with a high number of cases, high severity of illness and consequently high death toll.
History of Influenza Pandemics
During the 20th century, the emergence of several new influenza A virus subtypes caused three pandemics, all of which spread around the world within a year of being detected.
- 1918-19, "Spanish flu,"
[A (H1N1)], caused the highest number of known influenza deaths. It was estimated to have killed more than 40 million people in less than one year, with peak mortality rates occurring in people aged 20-45 years. Many people died within the first few days after infection, and others died of secondary complications. Nearly half of those who died were young, healthy adults. Influenza A (H1N1) viruses still circulate today after being introduced again into the human population in 1977. - 1957-58, "Asian flu,"
[A (H2N2)], although milder, was estimated to have caused over 1 million deaths worldwide. The pandemic emerged in southern China when a bird and a human flu swapped genes, resulting in a new deadly virus. - 1968-69, "Hong Kong flu,"
[A (H3N2)], caused about 750,000 deaths worldwide. This virus was first detected in Hong Kong in early 1968. Similarities to the 1957 virus meant people had some immunity which helped reduce deaths. Influenza A (H3N2) viruses still circulate today.
Past history showed that pandemic influenza occurs roughly every 10 to 50 years, and may strike at any time.
Current situation
It is possible for another influenza pandemic to emerge and cause devastating tolls of illness and death worldwide, thus authorities across the nations are in preparation. Although it is not considered feasible to halt the spread of a pandemic virus, it should be possible to minimize its consequences through advance preparation to meet the challenge.
The Hong Kong Special Administrative Region Government adopts the following principles of preparedness to safeguard the health of the community:
- Reduce risk of human infections,
- Early detection of influenza pandemic, and
- Enhance emergency preparedness and response for influenza pandemic.
Prevention
When a pandemic strikes, it may not be possible to totally eliminate the risk of infection. However, you can reduce the risk considerably if you are prepared for the following measures and adhere to them.
- Step up hygienic practices like washing hands and keeping the environment clean and maintain good ventilation.
- Avoid crowded or poorly-ventilated places.
- Wear a mask if you develop flu-like symptoms, when caring for the sick, and when visiting hospitals and/or clinics.
- Watch out for the latest situation of the influenza pandemic and further announcements from the government.
- Pay attention to and comply with guidelines issued by the government with respect to travelling, port health control and suspension of public events as needs arise.
WHO phase of pandemic alert for Pandemic (H1N1) 2009: Post-pandemic Period
In August 2010, the World Health Organization (WHO) announced that the world had moved into the post-pandemic period.
In the post-pandemic period, influenza disease activity will have returned to levels normally seen for seasonal influenza. It is expected that the pandemic virus will behave as a seasonal influenza A virus. At this stage, it is important to maintain surveillance and update pandemic preparedness and response plans accordingly. An intensive phase of recovery and evaluation may be required.
For WHO phases of pandemic alert, please click here.
* For further information, please go to Seasonal Influenza - Disease Information or Avian Flu (H5N1) - Disease Information.