MMR/autism: Have we fully investigated the risks?
点击量： 时间：2017-08-09 03:02:14
By Michael Day A CONTROVERSIAL study suggesting that autism is a rare side effect of immunisation against measles, mumps and rubella has led to calls for more research into the safety of multi-component vaccines. These immunise children against several diseases with a single jab. In the latest issue of The Lancet (vol 351, p 637), a team led by Andrew Wakefield of the Royal Free Hospital in London reports a study of 12 children with behavioural disorders and an inflammatory bowel condition. All were given the measles-mumps-rubella (MMR) triple vaccine and nine have been diagnosed as autistic. Wakefield believes that in rare instances, the MMR vaccine causes bowel inflammation, which in turn can trigger the extreme social withdrawal of autism. However, other experts say that the study is inconclusive. Frank DeStefano, a vaccine safety specialist at the US Centers for Disease Control and Prevention in Atlanta, says that it is difficult to determine in retrospect whether the symptoms of autism emerged only after the MMR vaccination, which is usually given between 12 and 18 months of age. DeStefano also points out that millions of people have been given the MMR vaccine. So if autism is a side effect, it is extremely rare. Given this – and the fact that measles, mumps and rubella are serious diseases – health experts urge parents not to spurn the vaccine. But Wakefield and other immunologists argue that the new study highlights the need for more research into the risks posed by multi-component vaccines. Some fear that they may “overload” the immune system of some infants. “With whole-organism vaccines you elicit a range of immune responses,” says Richard Le Page of the University of Cambridge. “This might in theory result in an immune response that is harmful.” But multi-component vaccines are popular with health officials, because they require fewer clinic visits. Britain’s Public Health Laboratory Service is now testing an acellular whooping cough vaccine to be given in a single shot with the triple vaccine against diphtheria, tetanus and polio, and possibly with the hepatitis B vaccine. Simon Murch of the Royal Free Hospital, one of Wakefield’s team, says that current monitoring regimes are inadequate to judge whether such vaccines are safe enough in the long term. “Extending our follow-up of vaccine safety is going to be important,” he says. Children given vaccines in trials are followed for just a matter of weeks to check for acute reactions. Once a vaccine is in use, it is left to doctors to report suspected adverse effects. DeStefano concedes that these checks may miss some adverse reactions. “They’re not going to tell us if they’re related to autism or some other disease that happens three years down the line,” he says. Wakefield wants the MMR vaccine to be replaced by individual vaccines given one year apart. But Britain’s Department of Health disagrees. “It would be irresponsible to leave children unprotected between vaccinations,” says a spokesman. However, the department has commissioned the Medical Research Council to conduct a review of the MMR vaccine’s link with autism, which will be chaired by John Pattison,