A Polio vaccine given to tens of thousands of children in 1998 contained serum from a donor who has been diagnosed with variant CJD, the Minister for Health and Children said yesterday.
However, because the donor's plasma was mixed with that of more than 63,000 others, the risk arising from it was "almost certainly" zero, Mr Martin said.
The vaccine was administered between January 15th, 1998, and January 30th, 1999. Not every child given the oral polio vaccine during this time received the product in question, which was manufactured by Evans/Medeva in the UK. About 40,000 children received a different vaccine manufactured by SmithKline Beecham.
Polio vaccine is given to children at the ages of two months, four months and six months, and a booster immunisation is given at primary school entry age. Adults travelling to regions such as China, sub-Saharan Africa and parts of Asia are also vaccinated against polio.
Variant CJD is the human form of BSE. There are now about 88 cases in the UK and one in the Republic.
Prof William Hall, director of the Virus Reference Laboratory, said yesterday that in his opinion there was "zero risk" of contracting the disease from the vaccine.
The component for which the donor's plasma was used was the human serum albumin. In tests with BSE-infected animals in the US, the filtering process used to produce albumin removed any infected material several steps before it was completed, he said.
The Minister, Mr Martin, said the announcement was being made because the public had a right to know and because of fears of a "sensational" leak to the media.
In all, 83,500 doses of the polio vaccine were distributed in the Republic. Dr Chris McNamara, the Department's GP adviser, said 50,000 to 60,000 of these were administered.
Helplines have been established by the health boards for parents who wish to find out if the vaccine was given to their children.
The Irish Medicines Board confirmed that early in 1998 it wrote to Evans/Medeva saying it no longer wanted it to use albumin derived from British donors in its vaccine.
Medeva asked for a period of grace to allow it to make the necessary changes, and this was granted. The company ceased using such albumin around November. The company indicated yesterday that albumin derived from British donors was also used in its products in the UK until late 1998.
Dr Frank Hallinan, director of the Irish Medicines Board, said the board would look into the question of whether any of the vaccine was supplied to the Irish market at a time when it would not have been distributed in the UK. At present, no vaccines in use in Ireland contain UK-sourced human serum albumin.
Two months ago another Evans/Medeva polio vaccine was removed from the market by the medicines board after the British chief medical officer recalled the vaccine in the UK on the basis of what he called an "incalculably small" risk of contracting CJD from the product. That particular vaccine used material derived from the foetuses of calves.
It emerged last night that the Taoiseach received one of the Evans/Medeva polio vaccines. Mr Ahern received the polio booster in September 1998, before an official visit to China.
He and at least two officials received the vaccine as they were travelling to a farm in China outside urban areas. Those travelling to urban areas only were not advised to receive the shot.
A Government spokesman said last night Mr Ahern had heard the news yesterday but was "not concerned".