Something odd is happening with measles. First of all, despite the fact that the UK has in place the triple measles, mumps and rubella vaccine, and enjoys an extraordinarily high coverage of vaccination among toddlers, cases of measles are going up.

The first statistic demonstrating this isn't surprising. Between June 1991 and June 1992, cases of measles among 10 to 14 year olds in Britain more than quadrupled, from141 to 578. As a result of human interference, in Britain, like America, measles is becoming a teenage disease, when the childhood vaccine wears off and the disease can do greater harm.

Most mystifying of all, though, is that even though this vaccine has been around for six years, cases of measles have gone up by nearly one fourth, or 22 per cent, according to a report from the Office of Population Censuses and Surveys.

In America, on the other hand, after the great measles resurgence of 1989-1991, cases of measles are drastically dropping. The Centers for Diseases Control happily attributes this to the tremendous push given the measles and combined vaccines at the height of the recent epidemic; vaccine coverage increased from an average of 66 per cent in the years before 1985 to 78 per cent in 1991.

However, a few statistics confuse this optimistic assumption. First of all, the CDC estimates that, based on retrospective surveys of coverage, approximately 800,000 to 2 million babies and toddlers who hadn't got their shots should have been susceptible to measles. In reality, however, only 9300 cases were reported among this age group. Although the average age of children catching measles is dropping (from a median age of 12 in 1989, the beginning of the epidemic, to an average last year of 4.9), nearly half of all reported cases are still among children over 5 most of whom should have been protected.

The CDC has to admit that the sudden drop in cases could have something to do with "an overall decrease in the occurrence of measles in the Western Hemisphere". It also may have something to do, they say, with the cyclic nature of the disease.

American medical critic Dr Robert Mendelsohn once said "diseases are like fashion, they come and go". This seems to be the case with polio, which is making an appearance in Canada.

These statistics provide more possible evidence that many vaccine programmes claim the credit for what is simply the tendency of illnesses to wax and wane. And that far from science having anything to do with finally stamping out polio or smallpox, both diseases that have decided, for the moment, to take a breather.