How close are we to getting a vaccine for Lyme disease?

Diana Moser has, to the best of her knowledge, not contracted Lyme disease, a welcome status quo that might be credited to the tick-repellant clothing she wears in the yard of her East LaHave, N.S., home, or to the insect spray she squirts on herself, or to just plain-old luck.

Or, it's possible the good fortune is due to what some are hoping is a "game changer" in the fight against the disease, which is caused by tick-borne bacteria and, if left untreated, can lead to severe heart, joint and nervous system symptoms.

Moser is one of dozens of people in Nova Scotia, and more than 9,000 in the eastern United States, Eastern Canada and parts of Europe, who are taking part in clinical trials for a vaccine against Lyme infection.

"I think it's incredibly important to have," she said of a vaccine, noting she knows at least four people who have contracted Lyme disease, including one who has had it multiple times.

"It's such a tricky disease, like when you get Lyme, so many things can happen. It causes joint pain, it causes inflammation. It really affects your system in a deep and abiding way."

There were more than 27,000 cases of Lyme disease recorded in Canada between 2009 and 2024, the majority of those in the last four years. Actual infection rates are higher, however, because cases go undetected or unreported, according to the federal government.

In the United States, over 89,000 cases were reported in 2023 to the Centers for Disease Control. In one study, researchers used insurance claims data to estimate that nearly half a million people a year may be diagnosed and treated for Lyme disease.

The vaccine furthest along the research pipeline is the collaboration between multinational pharmaceutical giant Pfizer and European vaccine company Valneva SE, with Phase 3 clinical trials scheduled to run to the end of December.

A Pfizer spokesperson said if trials are successful the company could potentially apply in 2026 to the U.S. Food and Drug Administration and the European Medicines Agency for approvals to market the vaccine. There is no timeline for a similar application to Health Canada.

The clinical trials have targeted areas where Lyme disease is endemic. Participants were chosen for their increased risk, including landscapers in tick-infested areas, people who do a lot of hiking or gardening, or who have dogs that routinely come home with ticks attached.

Like all participants, Moser doesn't know if she has been injected with a course of the real vaccine and a booster, or simply been given a placebo, although she hopes to learn which it is once the trials end.

Some, but not all, blacklegged ticks carry Borrelia burgdorferi, the bacteria that causes Lyme disease. The ticks are tiny, living in woods, shrubs and long grass, attaching themselves to humans or animals that brush past the vegetation and then feeding on their blood.

When they bite, some of their stomach contents, including the bacteria, are eventually discharged into the bloodstream. In most cases, the tick must be attached for at least 24 hours before a person is infected.