TORONTO -- Toronto Western Hospital is currently dealing with a COVID-19 outbreak  ‘likely’ caused by the Delta variant and health officials say some of those infected had been vaccinated.

The outbreak on a 6th floor area was first declared on June 17 and so far four patients and three staff members have been affected.

According to a notice sent out to University Health Network staff Monday morning, preliminary results show that the majority "are more than likely the Delta variant."

Some of those affected by the outbreak have had either one or two doses of a COVID-19 vaccine.

UHN said that all the cases so far are mild.

“I think it's important for everyone to recognize that none of the individuals who have picked up COVID have had any severe disease,” UHN infectious disease specialist Dr. Alon Vaisman told CP24. “They all have been either asymptomatic or mildly symptomatic as a result of the COVID.”

The hospital said that it remains critical to continue following infection prevention and control and public health measures, such as masking, social distancing, limiting gatherings and hand-washing to hold the virus at bay.

UHN said that it was sending out the notice to staff in order to encourage them to get family and friends vaccinated and to continue following public health measures.

“It is discouraging that the Delta variant can infect those already vaccinated but critical that we continue with our vaccination efforts so that we can avoid hospitalizations from COVID-19 infections,” the hospital wrote to staff.

Studies have shown that while the Delta variant, first detected in India, is more infectious than other variants that have been identified so far, vaccines are still highly effective at preventing death and serious illness in those who do become infected.

Vaisman said that while the infections are “concerning,” they also demonstrate that the vaccines are effective at preventing serious illness.

“The primary purpose of vaccination is to eliminate that risk of hospitalization or mortality, and to decrease that,” he said. “People getting vaccinated is the best tool we have available to us, it's the best tool we have to prevent what we had recently in the wave three.”

Speaking at a briefing on Ontario’s COVID-19 situation Monday afternoon, Dr. Dirk Huyer, who leads Ontario’s outbreak response said current outbreaks highlight the importance of vaccination.  

"Clearly, we want to ensure that we minimize any chance of outbreaks, specifically those in populations that may be vulnerable, given that people in hospital may have other illnesses and this is clearly something that we don't want to occur," Huyer said. "We know that the first dose of all the vaccines that we have- AstraZeneca, Moderna, and Pfizer,- all provide a lesser degree of protection from infection, from getting an infection, but do provide significant protection from seriousness of the illness."

Ontario’s Chief Medical Officer of Health Dr. David Williams said the outbreak is further evidence that “we cannot take the Delta variant casually.”

Vaisman noted that none of the vaccines are 100 per cent protective against mild or asymptomatic COVID-19, so it is “not surprising” to still see some cases in vaccinated individuals.

“The most important aspect is that none of them have developed any severe disease thus far,” he said.