Lewis Wolpert: 'The primary reservoir of the influenza virus is not humans but aquatic birds'

Flu is not only nasty, but even when one has recovered there is a lingering feeling of being unwell. Worse still, it is dangerous, especially for the elderly. In global epidemics – pandemics – about one third of the world's population becomes infected. I grew up on horrific stories of the great flu pandemic of 1918, which killed around 40 million people worldwide; in the United States alone, 675,000 people died. The majority succumbed to a secondary infection of pneumonia, as antibiotics were not yet available; many others died from lung damage.

In the UK, each winter, there are some 12,500 associated deaths. Where does influenza come from, and why is it so lethal?

Influenza was first described about 1,000 years ago. It has the capacity to vary, and so evade any immunity that has developed in a population. A virus is not a cell and this is why it is resistant to antibiotics. Viruses are a tiny package of genes and proteins, and can only replicate when they get into the cell. In the case of the flu virus, the genes are in the form of RNA (ribonucleic acid), which will be translated into DNA (deoxyribonucleic acid) when it gets into the cell. A reason for the great variability of flu is that the virus has eight RNA molecules that can be exchanged with other viruses when they are present in the same cell at the same time. So, even after 1,000 years, flu continues to generate new variants.

The primary reservoir of the virus is not humans but aquatic birds, where there are no obvious symptoms – they at least have learnt to live with each other quite happily. New epidemics of flu can occur when human and bird viruses get together in the same cell to create new infectious forms. It is also likely that other animals such as pigs help the viruses to survive initially. But birds are the key players, and this has been suggested as the reason why some epidemics began in Asia where there were large live poultry markets allowing intimate contact between birds and humans.

A future pandemic is inevitable. What can be done? In the US, the plans include surveillance,vaccination – if possible, of the whole population – and encouraging the closure of live poultry markets. It will also be important to continue studies to understand why the 1918 virus was so virulent, and affected those under 65 more than the older population. Indeed, the issue is complex, and some argue that the 1918 pandemic did not in fact have its origin in the East, since in the absence of air travel, how could it have spread worldwide?

The answer, they suggest, is that it had its origin at a huge British Army base in France. Many soldiers suffered from an acute respiratory infection not recognised as influenza. The demobilisation in 1918 could have provided ideal circumstances for the spread of the virus, as it undoubtedly involved an enormous number of new and intimate person-to-person contacts.

In the 1970s, the wisdom of the day when one got flu was to take aspirin or paracetamol, and a high fluid intake. Many people still think that this is the way, but, on the contrary, there is good evidence that certain drugs that act on the virus are quite effective if given early on. So, should it not now be possible to purchase such anti-viral drugs over the counter, instead of having the serious delay of waiting to see one's doctor? The price is low – around £3. Is it not both unreasonable and bizarre that we can buy lethally fattening foods, alcohol, and cigarettes over the counter, but not medicines with minor side-effects? At present, there is little that one can do when flu comes, other than be patient. You could, of course, try my almost certain cure – sing the National Anthem each morning, and you should be fine in three weeks. But much better, vaccinate, vaccinate. And avoid all those who are still singing.

Lewis Wolpert is professor of biology as applied to medicine at University College London