Unvaccinated people are "very exposed" to COVID-19 at the moment, Dr Colm Henry has warned.
The HSE Chief Clinical Officer says it's "not true" for unvaccinated people to think they have protection from other people who are vaccinated.
He was speaking amid the ongoing surge in COVID-19 cases, with over 3,000 new cases reported for the past three days.
Tánaiste Leo Varadkar said those numbers are expected to hit 4,000 in the coming days.
There's been a fresh campaign to encourage people to get vaccinated, and the HSE says they've seen a significant number of people coming forward for their first dose over the past few weeks.
Speaking on The Pat Kenny Show, Dr Henry said unvaccinated people simply aren't protected against the virus - especially due to the Delta variant.
He said: "If people out there are unvaccinated and think they have protection from other people who are vaccinated… that’s not true. You can still acquire it from someone who’s vaccinated.
“If you’re unvaccinated, you’re very exposed at the moment. This isn’t fear mongering - this is fact.
“Make your mind up, read the information: but my message is I would strongly advise you, for your own protection and wider community protection, to get vaccinated.”
Dr Henry said recent studies have shown vaccinated and unvaccinated people can have similar 'peak viral loads' if exposed to the virus - meaning vaccinated people could still spread the virus.
However, he noted the evidence is suggesting vaccinated people's viral load will reduce quicker.
Dr Henry stressed the "vaccine wall" is holding up in Ireland, and the intention is to make sure non-COVID care isn't disrupted like it was last winter.
Booster doses are due to start being rolled out to healthcare workers this weekend.
However, the WHO has again criticised wealthy countries for pushing ahead with booster campaigns while many people in the developing world - including healthcare workers - remain unvaccinated.
Dr Henry said Ireland's now targeting specific groups for boosters to "have the maximum effect".
He said Ireland has donated a million vaccines via the COVAX programme, with hundreds of thousands of AstraZeneca doses given to Uganda through a separate arrangement.
The HSE CCO also noted that Israel - which has rolled out widespread boosters - has seen a "big, big drop" in symptomatic cases of COVID-19.
He said: “Countries are trying to balance their own fears and vulnerabilities… even with the well-developed healthcare systems throughout Europe, none of them are able to withstand uncontrolled transmission of this virus - particularly if that vaccine floodwall isn’t there to defend them.
“Science is showing that… vaccines in the first instance appear to be holding up against serious illness.
"But with the antibodies... there’s a waning immunity."
He said it appears the waning means decreased protection against "acquisition of the illness and milder symptomatic illness".
New treatments are also now emerging to treat COVID-19, including pills developed by Merck and Pfizer.
The Merck pill was this week approved for use by the UK.
Dr Henry said Ireland will be entering a joint purchasing agreement with other European countries for that pill, but there's a need to wait for further evidence and EMA approval before it gets the green light.
He noted: “We certainly want to make sure the early promise is backed up by substantial evidence.”