TORONTO -- A fully-vaccinated long-term care resident is among those infected in the latest COVID-19 outbreak at a Peterborough nursing home.

One resident and two staff members have tested positive for the virus in the fourth outbreak at the Fairhaven facility since the start of the pandemic.

In addition to the resident, who has been immunized with both doses, one of the staff members who tested positive had received their first dose of the vaccine.

“It’s not 100 per cent,” said Dr. Anna Banerji, infectious disease specialist with the University of Toronto’s Dalla Lana School of Public Health.

“The vaccine isn’t going to prevent all cases of COVID, or prevent every single death, but it drastically reduces hospitalization and death.”

The severity of symptoms of the resident who tested positive is not known, though experts point out that elderly populations remain more susceptible to COVID-19 even after two doses of vaccine.

“We do know that the effectiveness of vaccines is lowered in that population,” Dr. Amit Arya, palliative care lead at Kensington Health, told CTV News Toronto.

“Specifically in long-term care homes, we have a population that is not just older, but people who have severe co-morbidities, people who have advanced incurable illnesses like heart failure, end-stage lung diseases, dementia, and frailty, where we expect the vaccine might not work as effectively.”

Public health officials believe that the partially-vaccinated staff member contracted COVID-19 outside the long-term-care home and then infected the resident.

“Many of the outbreaks are being caused by staff that are bringing in the virus from the community unknowingly and through no fault of their own,” Sinai Health geriatrician Dr. Nathan Stall said Wednesday.

“So this is another opportunity where we can shore up an additional line of defence, by maximizing vaccination among staff members.”

The affected Fairhaven resident is isolating, and all visits to the long-term care home have been suspended.

Public health officials have not released information regarding how long ago the resident or staff member who tested positive were vaccinated.