VANCOUVER -- A B.C.-based doctor is one of many drawing connections between COVID-19 and an increase in overdose deaths in the province.

The St. Paul's Hospital emergency room medical lead said the jump in overdoses in March and April was "definitely" related to the pandemic.

"COVID has caused a lot of collateral damage, and unfortunately, one of the most vulnerable groups is our substance users," Dr. Daniel Kalla said in an interview on CTV Morning Live.

He said the impact the virus has had on the province's other public health crisis is that some have been afraid to use safe injection sites, or with other users, because of the risk of transmission.

"Which is such a lower risk to them than using alone, which can be suicidal at times with this drug (fentanyl) and the terrible drug supply that we have," Kalla said.

Some are also hesitant to go into emergency rooms for the same reason, though Kalla said those without support systems often don't have many options.

"We are a last resort for them often, but we're sometimes the only resort as well," he said.

"We didn't see as big a dip in visits from our 'no fixed address' in Downtown Eastside community as with the other communities."

Kalla said another possible factor in the increase in overdoses in B.C. is the border closure.

Facing supply chain issues, local gangs are making their own mixtures, and users may be getting a different product than they're used to.

"It's cooked in these terrible labs with zero quality control and they play Russian roulette with their mixtures," he said.

"But on top of that, when your predictable source from places like China and Mexico are closed off, these criminals will do anything to make a buck, and work with whatever they have. So I think it's even more inconsistent in terms of the potency of the dose that's going out on the street."

Kalla was also asked about local initiatives in place in B.C., and a fictional book he's written based on his experience with the overdose crisis. Watch the full interview.