A decision on whether the Dublin Marathon can go ahead this year will be announced on June 25th.
Organisers say the vaccine is "key" to allowing runners and spectators take part in the annual race.
Last year 25,000 runners signed up to take part in the race and were promised a spot in this year's event.
While organisers say there's a "slim chance" all applicants will be permitted to take part this year, they are hopeful to get 10,000 or 15,000 runners across the finish line.
The event is due to take place on October 25th.