A second Covid-19 booster shot will be offered to adults aged between 18 and 49, the Health Service Executive (HSE) said.
People within the age bracket are invited to register for a booster shot on HSE.ie, as long as its been six months since their last vaccine, or since their last infection with the virus.
Boosters may also be available at pharmacies and GPs.
National Lead of the Covid-19 Vaccination Programme, Eileen Whelan, HSE said the move was in line with the latest advice from the National Immunisation Advisory Committee (NIAC).
"I encourage everyone to get their second booster dose," Ms Whelan said. "It will give ongoing protection from serious illness, and increase your immunity against infection from COVID-19, which we know tends to reduce after a period of months following your last vaccine."
HSE Chief Clinical Officer Dr Colm Henry said there was concern over the "steep rise" in cases of Covid, influenza and other respiratory illnesses at present.
"Our GPs and hospitals are working hard to support people, but we have seen a more than 100 per cent increase in cases of flu, and people needing hospital admission for flu.
"In the week ending on December 24th, we had 2,329 flu cases reported, compared to 1,174 the previous week. People needing hospital admission for flu jumped to 637, from 299 the previous week. COVID-19 cases increased to 3,809, compared to 3,118 the previous week, with 737 people in hospital with COVID-19," he said.
The news comes as a number of countries take measures against rising cases of the virus. On Thursday, European Union leaders held talks regarding China's decision to lift Covid-19 restrictions amid a wave of infections there.
The scale of the outbreak in China and doubts over official data have prompted countries including the United States, India, and Japan to impose new travel rules on Chinese visitors while others, including Britain, said they had no plan to bring back Covid testing for those coming into the country.
