The head of the HSE has called for the public to "galvanise" young people to help curb the spread of Covid-19.
Paul Reid said the country should avoid knocking down the youth of Ireland amid concerns of further restrictions following a growing number of Covid-19 cases.
It emerged last week that people aged 15 to 34 account for 40% of Covid-19 cases in the past two months, despite accounting for just a quarter of the population.
On Friday, acting chief medical officer Dr Ronan Glynn and his Northern Ireland counterpart, Dr Michael McBride, made a specific appeal to teenagers and people in their 20s and 30s in Co Donegal and Derry to reduce their social contacts.
Donegal moved to risk level three of the Government's plan to deal with Covid-19 following advice from the National Public Health Emergency Team (NPHET).
The restrictions will last for three weeks.
The chief medical officers said they were concerned about the significant proportion of cases in young people in Donegal and Derry, and asked teenagers and those in their 20s and 30s in particular to reduce their social contacts.
"Young people have made this country an even better place to live, in my book," Mr Reid tweeted this weekend.
"Marriage equality, climate change awareness and much more, all enabled by them.
"Again we put a weight on their shoulders to help us with Covid-19. Let's not knock, but galvanise them once again."
The Government has also imposed country-wide level three restrictions on colleges, which will see most lecturers moved online.
Higher education institutions are to adopt the same health measures already in place in Dublin for the next two to three weeks.
Minister for Further and Higher Education Simon Harris said on Friday that colleges and libraries will remain open.
Taoiseach Micheál Martin voiced concerns earlier this week about the 18 to 34 age bracket, particularly as many students return to third-level colleges.
Mr Martin said college life will not be normal for students.