KITCHENER -- A Stratford woman says she's in a tough spot managing medication for multiple sclerosis that could impact the effectiveness of her COVID-19 vaccine.

Lindsey Martchenko was able to get her first vaccine dose in March.

"It felt great," she said. "Just a little soreness in the arm."

Every six months, Martchenko gets an infusion of Ocrevus, a medication to treat multiple sclerosis. She said without the medication, she could relapse.

"I could all of a sudden have mobility issues, I could all of a sudden lose vision," she said. "You have no idea. It's completely unpredictable."

Dr. Courtney Casserly, a neurologist working at the MS clinic at University Hospital in London, Ont., said the medication prevents inflammation in the brain and spinal cord. She also said it can hinder the build up of antibodies and make patients more susceptible to severe cases of COVID-19.

"(Patients are) more likely to end up in the hospital and more likely to end up on a breathing tube," Dr. Casserly said.

Patients on Ocrevus should be vaccinated 12 weeks or more after their last treatment and then resume treatment four weeks or more after being fully vaccinated, Dr. Casserly said.

For Martchenko, she said she's been left with a tough decision, because her next Ocrevus treatment is scheduled for May 11, with her next COVID-19 shot planned for July.

"(I’m) deciding between getting protected against COVID and risking a relapse," she said.

Martchenko said she's hoping health officials will let her get her second dose early so she won't have to be off her MS medication for too long.

"There are exceptions for other individuals, for example for things like transplant patients," Dr. Casserly said.

In a statement to CTV Kitchener, Huron Perth Public Health said it will continue "to follow the provincial direction on timelines for second doses," adding the province hasn't listed people with MS on the shortened interval list.

Martchenko could also switch medication, but Dr. Casserly said she's "reluctant" to move someone off a drug that's working well.

"It's been proven to work with me," Martchenko said.

The MS Society of Canada said people with MS should get the COVID-19 vaccine, adding the decision about when to get it should be made with a health-care team after assessing the patient's risk from the disease and the current state of their MS.