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What is a Pandemic? |
Information from the UK’s Chief Medical Officer states that: a pandemic is an outbreak of a disease that affects many hundreds of thousands of people across many countries. The current threat is from an influenza pandemic, however it is also possible for other diseases to have pandemic proportions such as HIV/AIDS and tuberculosis.
Influenza Viruses
Influenza viruses are named according to their exterior protein structure, based on two proteins, haemagglutinin (H) and neuraminidase (N). There are 3 different groups of flu viruses (A, B & C). Type A is the usual source of ‘ordinary’ flu epidemics and also infects birds and other animals, e.g. pigs and horses. This unique ability to jump the species barrier enables the type A virus to cause pandemics and has been responsible for previous pandemic outbreaks.
• ‘Ordinary’ flu epidemics kill between 500,000 and 1 million people globally every year.
For an influenza virus to be able to cause a pandemic, it is far more virulent than ‘ordinary’ flu and has distinctive characteristics causing it to be different from previously circulating strains. This novel subtype virus happens as a result of major genetic changes in the flu virus, known as antigenic shift, and has occurred sporadically throughout history.
• Influenza pandemics have occurred three times in the last one hundred years with approximately 20-45 million deaths worldwide.
A/H1N1
The current outbreak of swine flu has spread across enough countries for the World Health Organisation (WHO) to declare Phase 6 of its global influenza preparedness plan. This indicates that a global pandemic is under way.
Although derived from a known swine flu virus (H1N1), it is clear that the virus has mutated to become a new strain of flu transmissible between humans. At this time there is no vaccine available to combat this new virus and it is likely to be some months before one is manufactured. However, the virus has shown that it can be treated with anti viral medication.
We do not know how this virus will evolve over the coming months so it is difficult to gauge the potential rate of infection and virulence. H1N1 could continue to produce relatively mild flu symptoms or become more severe as well as spreading widely across communities.
A/H5N1
The potential future threat of a pandemic is from a highly pathogenic avian influenza or ‘bird’ flu (known as A/H5N1) in Asia where there have been widespread outbreaks in poultry. A/H5N1 was first documented in 1997 in Hong Kong causing severe respiratory disease in 18 humans six of whom died. Close contact with live infected poultry was shown to be the source of human infection. The outbreak was halted by the culling of chickens.
This strain has therefore demonstrated the ability to infect humans and is proving difficult to eliminate. Experts fear that the virus could either adapt, giving it a greater affinity for humans, or exchange genes with a human flu virus, thereby producing a completely novel virus capable of spreading easily between people, causing a pandemic. The likelihood of this mutation occurring is not easy to predict.
• A/H5N1 has shown the ability to mutate and acquire genes from viruses infecting other species, such as humans. |
WHO International Phases |
The World Health Organisation (WHO) phases describe the progression of an influenza pandemic. This is a global classification based on the overall international situation and used worldwide for planning purposes. The UK also has four levels of alert that become operational during WHO Phase 6.
To view the WHO International Pandemic Phases and UK alert levels, please click on the link below:
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| WHO International Phases & UK Alert Levels |
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