Sean O'Grady: Why mass immunisation is essential

Whatever the cost to the taxpayer of immunising people against swine flu turns out be, it will almost certainly be money well spent if it helps slow the spread of the disease and minimises the gigantic damage to the economy it is likely to inflict in terms of days off sick and lost output.

It is almost anyone's guess what that cost would ultimately be, but even the most conservative estimates have put it as high as 1 per cent of the UK's national income, which equates to about £15bn, or about £500 for each member of the working population. These figures are based on what the Department of Health in the summer called a "reasonable worst case scenario" – an infection rate of 30 per cent and an average absence from work of seven working days.

More morbidly, on the best guess of the swine flu death rate, we would lose about 6,000 people permanently from the working population, representing a lifetime loss of output of perhaps £2.4bn between them.

However, that may not be the whole story. Factor in additional costs for the depressing effects on consumer confidence and spending, and on travel and tourism, and the economic carnage would be much greater – 2 or 3 per cent of GDP, or approaching £50bn. That would be enough to push the economy back into the depths of recession, causing some high-profile corporate casualties.

Against that, some workers will do the work of others, and spending on health care and medicines would rise to partly compensate for these effects, but not by much.

It is fair to point out that other supposed health "shocks" to the economy such as avian flu, Sars, terrorism and foot and mouth were much exaggerated. But the economic message remains clear: the risks to the economy of swine flu are easily severe enough to justify a mass immunisation programme now.