There are an estimated 244,000 booster doses of Pfizer Covid vaccines and 160,000 of Moderna in stock due to expire in the next two weeks.
This may be down to high infection rates in recent months, along with short shelf lives for jabs.
HSE guidelines state a person cannot get boosted until 90 days have passed from their positive test.
GP in Galway Primary Care Dr Brian Higgins thinks some patients are less flexible with the appointments too.
Mr Higgins said: "People are maybe less able to work around our timetable and might postpone their vaccine if it didn't suit them or if they didn't want it on a Monday in case they were sick Tuesday and Wednesday or felt unwell after it."
He added: "It's not as much hesitancy as such but definitely a bit less flexibility from some patients in making themselves available to get the booster."
