London's largest shelter for men and women is housing people in the chapel and in isolation rooms as it deals with the first COVID-19 outbreak since the pandemic began.

The Salvation Army Centre for Hope said Friday that 20 residents and nine staff members have tested positive for the virus, with dozens of others in isolation.

The outbreak comes during a cold weather alert that is driving people living rough to seek out shelter beds.

"We're starting to look at cordoning off some wings so that you can put people together and keep them away from everyone else. We're doing everything we can to isolate as much as possible," said the centre's executive director John DeActis.

But finding that space is not obvious. DeActis says the Centre for Hope is at capacity and it is extremely difficult to contain the spread in a congregate living setting.

The Omicron variant is highly contagious and has overwhelmed testing capacity, driving hospitalization rates to new highs, including in London, where 153 patients with COVID-19 are being treated as of Friday.

Other institutions in the London area are also battling outbreaks, according to the Middlesex London Health Unit, including the provincial jail, seven wards at the London Health Sciences Centre and multiple long-term care homes.

This week, the health unit started using its mobile vaccination unit to target London's homeless population, sending it to shelters and settings where people meet. DeActis said it has been to the Centre for Hope or in the downtown area three times this week.

"We were aware before Christmas that about 60 per cent of our residents were vaccinated, but in the homeless sector, we understand it's below 50 per cent in total. We certainly educate our residents, but it's really up to them."