This year's Dublin marathon scheduled for 25 October was cancelled on Tuesday despite Ireland's move to lift coronavirus lockdown measures, indicating potential long-term disruption caused by the outbreak.
Ireland plans to have fully lifted restrictions well before October, in a staggered process that began on Monday.
But organisers indicated the race - which had 22,500 entrants last year - would still not go ahead because of safety fears.
"We made the difficult decision in the best interest of the health and well-being of all those involved in making our events such a success from runners, supporters, volunteers, sponsors, to suppliers," said race director Jim Aughney.
"We explored many alternatives for running the events safely but ultimately none were viable."
Ireland's five-stage "roadmap" to reopen the nation is due to be completed in August, when the current ban on mass gatherings of more than 5,000 people is set to expire.
The cancellation suggests coronavirus fallout may last longer than suggested by official plans and could hit similar events.
The London Marathon, which attracts tens of thousands of runners, has been postponed until October 4.
"We need to be aware that we will continue to be in the acute emergency phase of this crisis for some time with further waves an ever present danger," the health department Secretary-General Jim Breslin told a special parliamentary committee on the crisis.
"This is not a one, a two or even a three-day storm, after which we move to a recovery phase. The acute phase of this crisis will definitely be measured in months and most probably in years."
Ireland has suffered 1,547 deaths from Covid-19, according to the department of health.
On Monday the number of daily deaths had fallen from a peak of 77 to just four.
"We have suppressed the virus and limited its impact on public health," said chief medical officer Tony Holohan on Monday.
"We need to sustain this in the weeks and phases ahead."