The director general of the HSE Paul Reid has apologised to the 2,000 people who tested positive for Covid-19 who were asked to forward a text to their own contacts.
Mr Reid described the situation as "unfortunate" and "concerning".
The Government has come under fire for the situation, which emerged in recent days.
Despite recruiting an extra 70 contact tracers per week, the “huge surge” in cases in the past 10 days “did catch us", he said, speaking on RTÉ radio.
The recruitment process had not caught up with the surge in cases, he said. The recruitment campaign had started on September 7 and some 2,000 people had applied and 800 interviews were held over five weeks.
There are now 500 people working in contact tracing and the HSE plans to build this up to 800 in the next few weeks.
“We will get 70% of decisions right; the most important thing to do is to make a decision,” he said, paraphrasing the WHO's Mike Ryan who had said that if wait you won’t get perfection.
But the 30% of wrong decisions would cause a lot of angst, he warned.
Mr Reid acknowledged that he should have communicated the decision to advise people to do their own contact tracing with the Taoiseach, with whom he is in regular contact.
It was a decision that had to be made about the operation and it was one he stood over, he said. Every decision that was made with regard to health “gets political”.
He added that the story broke in the media as staff were trying to deal with the issue.
It had been an unfortunate situation and he regretted that it had happened.
Mr Reid said that each of the 2,000 people who had been asked to do their contact tracing would have an average of four close contacts, the majority of whom were close family members.
The HSE will continue to build up lab capacity, tracing capacity and ICU capacity, he said, and the Government had offered its full support to provide resources for “what we need, if we need it.”
“But the only way we can reverse this is to reduce community transmission. The public can turn this around.”