Health boards throughout the Republic have begun a search for up to 30,000 people - mainly infants and children - who may have been treated with an inferior tuberculosis vaccine.
The Irish Medicines Board is stressing, however, that there are no safety issues related to the vaccine, "other than a possible reduced effectiveness".
This is the second time in two months that the board has expressed dissatisfaction with vaccines supplied by Evans Vaccines Ltd, of the UK.
In the initial case, up to 2,500 people were thought to have been treated with a vaccine which may not have reached the desired potency.
However, yesterday the Minister for Health, Mr Martin, said a second batch, distributed in the Republic between April 2000 and April 2002, had been found to be less than satisfactory. The Irish Medicines Board has already suspended the licence issued to Evans Vaccines.
Around 30,000 children and adults who received a BCG vaccine between April 2000 and 2002 are now to be examined by their local health boards to see if the vaccine has been effective.
According to Dr Pat Doorley, deputy chief executive officer of the Midland Health Board, the search to identify the patients will, for most health boards, be a tedious process of trawling through manual records and checking against batch numbers.
Once identified, patients who may have received the vaccines will be invited to return for testing. Visual testing will involve checking for slight scar formation which would indicate the vaccine had been effective. If scarring is not evident then a "Mantoux" test will be carried out, and repeated if necessary. Following these three steps, if a patient still tests negative, he/she can be re-vaccinated.
Alternative effective supplies of the BCG vaccine have been secured and are being delivered to the health boards. More will be available in September.
The Fine Gael spokeswoman on health, Ms Olivia Mitchell, said she had been told that a hepatitis C vaccine she had been given had lacked potency.
According to Ms Mitchell the situation was further disturbing evidence of a lack of quality assurance and she called on the Minister to "treat this whole matter with a sense of urgency and ensure the integrity of the supply chain".
Yesterday the Western Area Health Board and the three area health boards in the Eastern Regional Health Authority said they were unable, as yet, to quantify the number of people treated.