Concern about the measles, mumps and rubella (MMR) vaccine was raised again yesterday when American research claimed to show a high incidence of neurological problems linked with the jab. The findings were dismissed by the Department of Health, which described the research as "seriously flawed".

Neurological problems after the MMR jab were five times higher than after the DTP (diphtheria, tetanus and pertussis) combined vaccine, said US doctors who analysed data from the vaccine adverse events reporting system between 1994 and 2000.

The researchers, Mark and David Geier, concluded that the marked increase in problems afterMMR was not sufficient reason to ban the vaccine but they called instead for it to be reformulated using dead instead of live forms of the virus. They saidparents should be offered the option of having their children given the vaccinations singly.

However, the findings, published in the online edition of International Paediatrics, were challenged by the Health Protection Agency. Dr Mary Ramsay, a consultant epidemiologist at the HPA, said: "This research is seriously flawed - it compares children of different ages who have received different vaccines and the conclusions are incorrect."

She said MMR was given at 15 to 18 months of age whereas DTP vaccinations were given at two, four and six months. The first signs of autism, however caused, typically appear during the second year of life.

"Regardless of the other weaknesses of the data, the failure to compare children of the same age is enough to explain the apparent excess of cases reported in the MMR group," she said. She added that the findings contrasted dramatically with other studies that have used valid methods and found no increased risk of autism following the MMR jab.

A Department of Health spokesman said the Committee on Safety of Medicines had looked at past research by the same authors using similar methods and concluded this kind of analysis could not be used to determine levels of adverse reactions and compare different vaccines.

"The conclusions concerning the association between MMR and DTP vaccine and the outcomes studied cannot be justified," he said.