Ontario health units are recommending stronger precautions against COVID-19 as infections rise, including advice to limit indoor holiday gatherings to fully vaccinated guests other than young children.The guidance comes as Ontario’s cases continue an upward climb — 1,290 new infections were reported Thursday — more cases of the Omicron variant crop up, and the province’s science experts predict the health system is likely to be strained in the coming weeks.Three public health units in southwestern Ontario issued joint recommendations Thursday, saying residents should limit social gatherings and work remotely if possible.