Britain has almost forgotten what killers infectious diseases can be. Smallpox has been eradicated and is now regarded as a potential terrorist weapon rather than a natural threat.

HIV/Aids, despite the massive advertising campaigns of the 1980s, is still, wrongly, regarded by many as a danger only to homosexuals or those who have liaisons with people from certain parts of the world: an attitude that may yet create a disastrous health crisis.

Sexual diseases generally are regarded by most people as a lifestyle issue.

Other exotic diseases may yet be on their way, although West Nile virus and other insect-borne infections are still largely other countries' problems.

Most of our worries are now confined to whether the annual flu jab will protect us against feeling awful.

But childhood immunisation has become an ever more delicate political problem. Babies do often get grizzly after a jab. Governments add more and more injections to the vaccine schedule and parents increasingly speak of their sense of guilt at putting their children through an unpleasant experience.

Public health specialists talk of herd immunity, the need to protect the population at large. They seek to convince even parents with doubts about the efficacy or safety of vaccines of their responsibility to inoculate their children for the greater good.

Polio, once a killer here, was still disabling thousands after the second world war. The oral vaccine introduced in 1962 brought a huge fall in cases. It is a remarkable fact that most of very few cases now reported in this country are linked to the vaccine meant to prevent it, but that risk was always outweighed for public health specialists by the evidence of rapidly dwindling disease.

Only now, when polio has nearly been eradicated across the world, is an even safer vaccine being introduced.

Public health specialists thought they had a good story to tell this week, but a newspaper journalist doing her job revealed the plans for a new combined vaccine earlier than they had intended.

By yesterday the government's advisers were in effect blaming the press for ruining it all by concentrating on the safety of mercury preservatives, when the replacement jab will have fewer constituents which may cause red arms and high temperatures.

They want no repeat of the MMR controversy, which sent vaccination rates among two-year-olds well below 80% - less than 60% in parts of London.

The recent discrediting of the report which caused the fear has given leaders of the vaccination programmes some comfort. But it was not the first time that scares had made inoculation rates tumble. Things were far worse in the late 70s and early 80s when doubt was raised about the efficacy and safety of the whooping cough element in the triple diphtheria, tetanus and pertussis jab.

Immunisation rates plummeted far further than in the MMR crisis; indeed that and the salmonella in eggs affair were key factors in officials playing down the looming BSE crisis and its possible health implications in the late 80s and early 90s.

The problem is that parents think of their children as individuals they want to protect while governments concentrate on the greater good. But Philip Minor, head of virology at the National Institute for Biological Standards and Control, says the split exists between doctors and public health officials, too.

"They like to do things that benefit the patient," he said. "If you have a patient on your hands and you give that patient penicillin, for instance, and the patient gets better, it is easy. You think, 'Thank you, thank you, doctor', with tears in your eyes.

"If you have a healthy baby and you give it immunisation and it does not get anything, do you go back to the doctor and say with tears in your eyes and say, 'Thank you. My baby did not get measles because you gave it the vaccines'? No, of course, you don't."

The government admits that some patients suffer vaccine damage: the Department for Work and Pensions runs a vaccine damage payments scheme.

But despite all the preparation for the launch of a new vaccine, at 5pm last night the government could not say how many payments had been made, what they totalled and how many claims were outstanding.

The individual still seems to be small beer.