A/H1N1 influenza: questions and answers

doi:10.1136/bmj.b1849

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Rebecca Coombes, associate editor, BMJ

rcoombes{at}bmj.com

The pandemic alert level has been raised to phase 5—just one level short of a full pandemic—by the World Health Organization. As influenza A/H1N1 spreads quickly from its origins in Mexico, Rebecca Coombes assesses the threat and our levels of protection

What is pandemic flu?

The term pandemic relates to the virus’s geographical spread rather than its severity. A flu pandemic is an ongoing worldwide epidemic caused by a novel influenza virus that infects a large proportion of people lacking immunity to that virus. It is at this point that the World Health Organization raises its alert level to 6. The three flu pandemics of the 20th century were in 1918, 1957, and 1968. The current phase 5 is characterised by “human to human spread of the virus into at least two countries in one WHO region”—a strong signal that we are on the brink of an epidemic and that the time to finalise plans is short.

Is it too late to stop a pandemic?

Richard Coker, professor of public health at the London School of Hygiene and Tropical Medicine, said in a BMJ editorial on 30 April that containment is probably not feasible, given the widespread presence of the virus across many countries (BMJ 2009;338;b1791, doi:10.1136/bmj.b1791). So far, cases are occurring in countries with robust surveillance systems. He pessimistically wonders if this is because cases are not coming to light in countries with poorer surveillance systems. Are we seeing only a part of the global picture? It is harder for developing countries to detect and mitigate the effects of a new flu virus, because they have low or nonexistent stocks of antivirals and limited access to an effective vaccine once it is produced.

How severe is this flu? How does it compare with seasonal flu?

The situation is unpredictable, and it is dangerous to second guess what might happen next. So far the case fatality rate is unknown. Each year seasonal flu …