— By Richard Woodman

LONDON (Reuters) - Thousands of children might be at risk of measles, mumps and rubella because two private clinics in Britain did not followed correct immunization procedures, the Department of Health said on Tuesday.

In an urgent message to all family doctors, the department said children who had received separate jabs against the three diseases at the two clinics should be re-immunized with the combined MMR jab.

"The present estimate is that this could involve up to 40,000 immunizations going back over a 10 year period," said Dr David Salisbury, head of the department's immunization and communicable disease team.

Demand for single MMR vaccines in Britain has risen following controversial research suggesting that the combined jab might be linked to an increased risk of autism.

Despite official reassurances that the research was flawed, some parents were so anxious, they paid private clinics to give their children the single jabs.

Salisbury said the two clinics involved, at Elstree Aerodrome in Hertfordshire and Hillsborough Arena in Sheffield, had closed as they were not registered with the National Care Standards Commission.

The problem came to light earlier this year but at the time it was believed that just over 1,000 children had received vaccines that were not properly made up or administered during the second half of 2002.

More information had now become available showing that the "aberrant" immunization practices began long before.

"Our two greatest concerns are that the clinics had not followed the correct procedures recommended by the manufacturer for making up and administering the vaccines," Salisbury added.

He said batches of vaccines were made up in advance. "This is not normal practice and might have led to the vaccines being less effective that normal.

"This means that some children who have been vaccinated may not be adequately protected against one or more of the diseases for which they received the vaccine."

Salisbury said the second worry was that the vaccines could have been contaminated because of the way they were prepared.

"This could have increased the risk of children suffering bacterial infections from the immunization or greater side effects to the vaccines."

The health department said that starting on Wednesday, it would use advertising and the media to advise parents who had used the two clinics to have their children properly revaccinated with the triple MMR jab.

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