The Government has urged people to start restricting their movements from today if they have plans to spend Christmas Day with vulnerable family members.
Senior civil servant Liz Canavan warned it would not be enough to limit contacts in the few days leading up to Christmas.
Ms Canavan, the assistant secretary-general at the Department of the Taoiseach, said people may have to postpone meals with friends until after Christmas.
She said: "It's now two weeks to Christmas Day and while I am sure you are already planning, but if you haven't now is the time to really start thinking about how you want to spend your holidays.
"This is especially the case as it has implications for how you spend the next two weeks.
"We are trying to get to 2021 safely. We want to avoid another spike in the virus. We know a vaccine is on the way for us, but a vaccine is not here yet and just because it is on the way doesn't mean we have any kind of immunity over the Christmas season.
"This means we must get the virus at the levels we have achieved in the last number of weeks or lower.
"To do this we must limit the number of people we spend time with to a very small circle.
"With two weeks to go from today, remember if you have plans on spending time with people who are vulnerable to Covid-19 over Christmas, you should be restricting your movements from now.
"It won't be sufficient to start limiting your contacts in the couple of days before Christmas. That means you might have to postpone that meal with friends until after Christmas and it will mean avoiding crowds."
Ms Canavan urged people to think about their contacts and prioritise their activities around a small group of people.
"Chose only those who are really important to you," she added.
"To sustain this level of freedom, keep the size of our social spheres to a minimum.
"Every contact counts."
She also pointed to reports of spikes of Covid-19 cases following Thanksgiving in the United States, adding "we don't want that here".
"Let's learn the lessons of other countries and be determined not to repeat what happened there," she added.
Meanwhile, HSE boss Paul Reid advised the public to "err strongly" on the side of what's safe.
He tweeted: "There is good light ahead as we plan for a vaccine roll out. But it will take time.
"In the meantime we all need to be realistic and make good judgements between what's possible and what's safe.
"Please err strongly on the side of what's safe and we'll get there."