Confidential documents on the introduction of the MMR vaccine should be released by the Department of Health, says the Information Commissioner.
Richard Thomas ruled that their release was in the public interest, despite months of foot-dragging by officials.
He said minutes from three committee meetings before the introduction of the Measles Mumps and Rubella jab in 1988 should be published under the Freedom of Information Act.
Some of the controversy surrounding immunisation has been fuelled by a ‘perceived lack of transparency’, he said.
'Ultimately, knowing who said what and whose opinions were taken into account will facilitate greater openness, accountability and transparency,' he said.
The information is likely to include data from the pre-licensing studies of MMR before the nationwide immunisation began in 1988.
The ICO said it had not received compelling evidence to suggest the commercial interests of the DH or drug companies was under threat.
The ruling also criticised the length of time the Department of Health took to correspond with the ICO, the late application of exemptions and the very generic nature of their arguments.
The Department has 35 calendar days to release the requested material.
Some parents boycotted MMR because of a supposed link with autism and bowel disease, following a controversial 1998 study by Dr Andrew Wakefield and colleagues published in the respected medical journal The Lancet.
British medical and Government experts blame Dr Wakefield's research for sparking a public health scare and say worldwide research has debunked his work.
Jackie Fletcher, who runs the vaccine awareness group Jabs, said parents who believed their children were damaged by MMR, often with debilitating gut problems, wanted to know the basis on which the vaccine was originally approved.
They had been kept in the dark too long, she added.
'We want to see what the evidence was and how long the vaccine was tested for before it was used nationwide' she said.