Immunocompromised Ontarians can book appointments for a fourth dose of a COVID-19 vaccine starting tomorrow.

Ontario's chief medical officer of health says the province has already started giving out fourth doses in long-term care homes, retirement homes and other congregate settings.

Dr. Kieran Moore says in order to further protect vulnerable populations, people who are moderately to severely immunocompromised can book a fourth dose starting at 8 a.m. Friday through the provincial vaccine contact centre.

Ontario is reporting 3,630 people in hospital Thursday due to COVID-19, and 500 people in ICU -- an increase in hospitalizations from 3,448 people the previous day, and five fewer people in intensive care units.

Moore says he anticipates Omicron will peak in Ontario in the next few weeks, predicting a difficult rest of the month followed by a better February and March.

The province also reported 35 new deaths Thursday from the virus.

Moore said provincial health officials are trying to determine what is behind large numbers of deaths reported recently, but said many will be due to the previous wave of Delta, a variant that a higher virulence, and some will be attributed to Omicron -- shown to be less severe --because there is such a higher number of cases.

There are 275 people on ventilators due to COVID-19, 10 more than the previous day.

There are 9,909 new COVID-19 cases reported, though Public Health Ontario has noted that the total number is likely higher due to testing policy changes.

Provincial data show 82 per cent of Ontarians aged five and older have received two doses of a COVID-19 vaccine and 88 per cent have at least one dose.

This report by The Canadian Press was first published Jan. 13, 2022.