Doctors on both sides of the border have renewed their calls for coordinated action to tackle high levels of Covid-19.
It comes as coronavirus case numbers in the north west continue to rise.
The rate in Londonderry and Strabane is the highest in Northern Ireland - that's mirrored across the border in Co Donegal, where officials are dealing with a number of spikes.
"People have let their guard down," said Dr Tom Black of the British Medical Association.
"They're mixing too much, they're passing the infection around, we've a lot more young people in the north west as a proportion of population.
"If you have a lot of infections in the community, you run the risk of mutations, and mutations can bypass the vaccines."
Health Minister Robin Swann has raised concerns about the north west with his counterpart in Dublin, Stephen Donnelly.
Reducing non-essential cross-border travel is a topic for discussion - Mr Swann says working together is key.
"At this minute in time it's how both communities work together to really drive down the spread of the Covid-19 infection," he said.