Vaccine Arthur Allen WW Norton, 15.00, 512pp

WHAT is the most important medical advance of the last 160 years? When the British Medical Journal put that to its readers recently they responded in their thousands. Sanitation topped the poll, followed closely by antibiotics and anaesthesia. In fourth came vaccines. While a similar poll of lay people might have agreed on the first three, would they have ranked vaccines similarly highly?

It seems doubtful. Vaccines have never had the kind of support that, say, antibiotics enjoy. Although vaccination has saved countless lives it remains controversial, driven by political imperatives, testing our faith in medical authority and our own judgement.

One of the enduring puzzles of the great MMR scare is not how it started . . . the 1998 paper in the medical journal Lancet linking the triple jab with bowel disease and autism is well known . . . but how it was sustained. Why did parents continue to doubt the vaccine in the face of repeated reassurances from medical authorities and in the almost complete absence of evidence to the contrary?

At least part of the answer is to be found in this enthralling book.

Though it does not discuss the MMR controversy in detail, it demonstrates how, through its 300-year history, the benefits of vaccination have been oversold and risks underplayed. The eagerness of authorities to protect public health has often blinded them to the risks of the vaccine.

In April 1947, New York registered its first death from smallpox in 35 years. A rug importer from Mexico had carried the virus to the city and caused panic. In three weeks more than six million New Yorkers were immunised against smallpox, jamming hospital clinics and queuing for hours . . . all entirely voluntarily . . . after the city's health commissioner announced his intention to vaccinate the city.

Yet by isolating and vaccinating each contact the outbreak was contained within days and the disease ultimately infected just 12 people. Meanwhile, six died from brain inflammation caused by the vaccine and 100 suffered serious injuries such as encephalitis.

In 1954, huge excitement greeted the launch of the Salk polio vaccine against one of the most feared childhood diseases.

But it soon became clear the version from Cutter Laboratories was crippling children. The vaccine had become contaminated by a live virus which infected up to 220,000 people, made 70,000 ill, and was linked to 164 cases of severe paralysis and 10 deaths.

The Cutter incident inspired major reforms. But they could not prevent vaccination's use as a political weapon. In December 2002, George W Bush rolled up his sleeve to be vaccinated against smallpox . . . a disease eradicated in 1980. He was launching a campaign to immunise 10 million health workers against biological warfare. Yet by 2005, fewer than 40,000 had come forward. Just as the Bush administration had failed to find weapons of mass destruction in Iraq, health workers saw the smallpox campaign as an unjustified attempt to build national consensus by stoking fear.

This is a fascinating, meticulously researched history which is admirable for its evenhandedness. In this fevered debate it is rare to find an author prepared to examine arguments without taking sides. Yet the moral of Allen's story is clear. By eliminating many diseases, vaccines have become a victim of their own success. Vaccination is no longer seen as a necessary rite of passage but a matter of choice, even though each person who vaccinates their child helps protect every other child.

Risks must be set out, but individuals must recognise that complete personal responsibility is unattainable. By accepting vaccination, we all help look after one another, as we must. That, as Allen says, is our social contract.

Jeremy Laurance is health editor of The Independent