Ar Ŵyl San Steffan yng Nghymru, daeth mesurau lefel rhybudd dau newydd i rym ar gyfer busnesau a chanllawiau wedi'u diweddaru a'u cryfhau i helpu pobl i gadw'n ddiogel gartref mewn ymateb i'r don omicron a ragwelir.
New alert level 2 measures for businesses and updated and strengthened guidance to help people stay safe at home came into effect on Boxing Day in Wales in response to the predicted omicron wave.