What is a pandemic?

jamesb-uk

If a pandemic is a disease affecting a large number of people over a very large area, does that mean that 'colds' and seasonal flu are pandemics? How many people have to be affected before something becomes a pandemic, and could a pandemic virus/bacterium theoretically produce no symptoms?

Moridin

A pandemic is a large scale outbreak of a dangerous pathogen affecting a large amount of people over a large geographical region, or more precisely in several WHO regions. Typical features of seasonal influenza is small, gradual changes and some natural immunity. For pandemic influenza, we are talking about a global outbreak of a new strain that humans most of the time completely lack natural immunity against. Therefore, seasonal influenza cannot properly be considered the same as pandemic influenza.

http://www.who.int/csr/disease/avian.../en/index.html

Phase 5 is characterized by human-to-human spread of the virus into at least two countries in one WHO region. While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short.

Phase 6, the pandemic phase, is characterized by community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5. Designation of this phase will indicate that a global pandemic is under way.

As for your question regarding whether it is possible for a pandemic pathogen to only produce asymptomatic carriers, a lot of the time the symptoms created by the pathogen and the body's response helps to spread the pathogen, such as coughing, sneezing and so on. It can be considered a general rule that it is not likely that a pandemic pathogen would produce nothing but asymptomatic carriers. This is because pathogens that spread better than others will produce more copies of itself that can infect others, provided all other factors are negligible, so this type of pathogen would be selected for over time.

jamesb-uk

So whether a disease is defined as a pandemic has no relation to the severity of the symptoms?

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jamesb-uk	What is a pandemic? Tweet If a pandemic is a disease affecting a large number of people over a very large area, does that mean that 'colds' and seasonal flu are pandemics? How many people have to be affected before something becomes a pandemic, and could a pandemic virus/bacterium theoretically produce no symptoms?