Measles could re-emerge as a constant threat in Britain because many parents, fearing possible side effects, don't get their children vaccinated, researchers say.
In a study appearing in the journal Science, British researchers report that the level of vaccinated children in Britain has dropped below 85 percent and that this rising number of unprotected youngsters is responsible for a recent surge in the number of measles cases in England and Wales.
If this trend continues, the authors suggest, measles could become firmly entrenched among the population and a constant source of sickness.
A decline in vaccinations "will lead to increasingly large outbreaks of measles and, finally, the reappearance of measles as an endemic disease," the authors state in the study appearing in this week's edition of Science.
The study was written by researchers at the Royal Holloway University of London, Imperial College in London and the government's Health Protection Agency.
In 1988, Britain began a childhood vaccination program using a combination vaccine that protected against measles, mumps and rubella. By 1998, about 91 percent of the nation's children were protected.
But shortly after that, some researchers reported they had found evidence that the MMR vaccine could cause serious side effects in children. At least one British physician, Dr. Andrew Wakefield, claimed that the vaccine was linked to autism, a serious mental disorder that develops in childhood. He made frequent public comments and attracted widespread news media attention.
Since 1998, many parents in England and Wales, as well as Ireland, stopped getting their children vaccinated with MMR.
The drop in vaccinations "has coincided with a number of large measles outbreaks," the authors said in Science. Later the study noted: "In their attempt to avoid the perceived risk associated with vaccination, parents' behavior collectively results in a substantial increase in the real risk of exposure to measles."
The study said vaccination levels continue to decline in Britain, even though "all of the claims of serious side effects (from the vaccine) have been refuted."
Dr. Samuel L. Katz, a Duke University pediatrics professor who is a prominent figure in research on vaccination policies, said the study should pose a cautionary tale for Americans.
Although there have been efforts by some organizations to discourage use of MMR in the United States, Katz said vaccination rates remain at about 98 percent after a number of studies by prominent medical organizations concluded that the MMR vaccine is safe and not the cause of autism.
"In this country, we've had 100 or fewer cases of measles every year recently whereas we once had millions," said Katz. Many of the cases that have occurred in the United States, he said, were contracted in other countries and imported to America, he said.
"Despite those importations, our children have been so well immunized that it hasn't been enough to fuel an outbreak," he said.
According to the federal Centers for Disease Control and Prevention, there were 19 reported cases of measles in the United States in 2002.
All 50 states require children to be immunized to attend public schools. But public health officials in the Britain use a different approach toward vaccinations, said Katz.
Instead of requiring MMR shots as in the United States, the British national health service encourages vaccination by rewarding doctors with bonuses if they meet certain quotas of vaccine protection among their patients.
A decline in immunization rates has had a significant effect in Ireland. Katz said that country, with a population of about 4 million, had more than 1,500 measles cases last year.
In one Dublin hospital, there were nearly 400 measles cases, with three deaths. Seven children required mechanical ventilation and 13 were treated in intensive care wards.
"They had measles the way it used to occur in this country," said Katz. "We don't ever want to see that again."
The last major outbreak in the United States came from 1989 to 1991 when there were more than 55,000 cases of measles. Twenty percent of the patients required hospitalization, Katz said, about one case in 500 resulted in death.
Katz said some religious groups in the United States are given exemptions from childhood vaccinations and that where children from such families group together, there have been outbreaks of disease.
For instance, he said a single elementary school in Colorado recently had eight cases of whooping cough, one of the diseases included in the MMR shot, after a cluster of unprotected children were enrolled there.
By Paul Recer