Professor Sam McConkey says 'about half the country' is moving in the wrong direction when it comes to the coronavirus.
The head of the Department of International Health and Tropical Medicine at the Royal College of Surgeons in Ireland (RCSI) was speaking after Donegal entered level three restrictions for three weeks.
The restrictions will be in place until October 16th.
Restaurants and cafés can stay open for delivery and takeaway, with outdoor dining for no more than 15 people.
Wet pubs will be allowed stay open in the county - but will only be able to serve outdoors on the same basis as restaurants.
While weddings planned for this weekend in Donegal will be allowed to go ahead on level two rules.
Prof McConkey told Newstalk Breakfast: "Unfortunately I think about half the country is moving in the wrong direction.
"We are going to need to see change in how we behave and how we congregate, and staying out of each other's homes and staying socially distanced to reverse that.
"I'm a strong believer in really controlling the spread of COVID completely on this island, and following the example of most of Australia and places like Greenland and the Faroe Islands, Jersey, Guernsey, not just New Zealand and China.
"But about 1.5 billion people in the world have completely controlled this, and we need to get into that group of the world - and expand the number of countries in the world that really don't have transmission of COVID.
Living with COVID ' fundamentally false' idea
"As I said in then Dáil a couple of days ago: this is like living with a tiger in your house - you can't live with it cause it comes back and bits you.
"So this idea of living with COVID is fundamentally false, as we've all just seen in the last three or four weeks, cause it just grows and ends up getting worse".
"I think the lockdown word is too binary and too divisive, I think we have to look at restrictions.
"[In] Donegal now many non-essential businesses are still open, so it's the not the same as what we had back in March.
"Our schools are open and we're committed to trying to keep education going.
"So we certainly have restrictions, and I would say escalating and changing restrictions, and that can be confusing at times.
"But to stay in our own homes isn't such a confusing piece of advice, so I don't see it as lockdown".
He said testing and tracing needs to be expanded, as does the COVID-19 Tracker app.
"It's clear that the app hasn't been adequate cause only 1.9 million people have had it downloaded.
"The problem is that many people don't have modern enough mobile phones: it doesn't work on the iPhone 5 or older Androids or on the Nokia Block.
"So maybe we need to be giving mobile phone devices that are modern enough to run it for all of us in the community.
"It's also not used for people under 16 years of age, and we know that many 10 to 16-year-olds do have an independent social life and go to school independently.
"So we could expand it more - what we've done in the last two months hasn't been adequate enough with our testing, tracing and app.
"So we need more and I'm hoping that we can improve on all those".
