Flagging the "early phenomenon", the HSE chief said it was "really important" people attend their booster appointments.
HSE chief Paul Reid has said some vaccination centres in Ireland offering booster doses of the Covid-19 vaccine are seeing "no-show rates" for appointments of 50%.
Reid was speaking during a HSE briefing on Thursday, when he urged eligible people to come forward for a booster shot when called.
Booster vaccinations are currently being administered to those aged over 60, the immunocompromised and healthcare workers.
Meanwhile, the National Immunisation Advisory Committee (NIAC) has recommended extending the booster programme to those aged 16-59 with underlying conditions and to those aged 50 to 59.
Reid said that while the booster campaign is progressing "really well", some centres are seeing high numbers of people not coming forward for appointments made.
"It's really important if you were offered a booster appointment, that you take it up," he said.
"We have seen some no-show rates in some centres, varying from 25 to 50%... We need those appointments utilised."
Reid said the reason for those eligible not coming forward could be because they feel they do not need a booster, having already received two vaccines.
However, he added: "The more people receive these booster shots when they are due... the smaller number of people we expect we will see when we are dealing with hospitals."
Meanwhile, the Health Protection Surveillance Centre has on Thursday been notified of 4,650 confirmed cases of Covid-19.
As of 8am on Thursday, 643 Covid-19 patients are hospitalised, of which 118 are in intensive care.
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Main image via Sam Boal / Photocall Ireland
