New Lyme Disease Vaccine Candidate Shows Major Progress

The most advanced Lyme disease vaccine candidate in over two decades has entered Phase 3 clinical trials, marking the furthest progress any such shot has made since the last human vaccine was withdrawn from the market in 2002. Developed by researchers at the University of Massachusetts Chan Medical School in collaboration with biotech company Valneva, the vaccine, known as VLA15, targets six strains of Borrelia bacteria responsible for Lyme disease in North America, and Europe.

Lyme disease, caused by the bacterium Borrelia burgdorferi and transmitted through the bite of infected black-legged ticks, affects an estimated 476,000 people annually in the United States alone, according to the Centers for Disease Control and Prevention (CDC). Early symptoms include fever, headache, fatigue, and a characteristic skin rash called erythema migrans. If left untreated, the infection can spread to joints, the heart, and the nervous system, leading to long-term complications such as Lyme arthritis or neurological disorders.

The only previously licensed Lyme disease vaccine, LYMErix, was approved by the U.S. Food and Drug Administration (FDA) in 1998 but was withdrawn in 2002 due to low public demand and unfounded concerns about potential autoimmune side effects, despite multiple studies finding no causal link. Since then, no human vaccine has been available, leaving prevention reliant on personal protective measures such as tick checks, repellents, and prompt tick removal.

VLA15 works by targeting the outer surface protein A (OspA) of the Borrelia bacterium. The vaccine induces antibodies that can neutralize the bacteria inside the tick before transmission to humans occurs. Unlike LYMErix, which targeted only one strain prevalent in the U.S., VLA15 is designed to protect against six serotypes of OspA found in Borrelia species circulating in both North America and Europe, broadening its potential geographic impact.

Phase 1 and 2 trials showed VLA15 to be safe and immunogenic, with a favorable side effect profile. The most common adverse events were mild to moderate and included injection site pain, headache, and fatigue. No serious safety concerns related to autoimmunity were observed in these early stages. The ongoing Phase 3 trial, launched in 2023, aims to enroll approximately 18,000 participants across regions with high Lyme disease incidence, including the northeastern and upper midwestern United States, Germany, and Sweden.

Participants receive three doses of the vaccine or a placebo, followed by a booster dose one year later. The primary efficacy endpoint is the prevention of confirmed Lyme disease cases over two follow-up years. Researchers will also monitor long-term safety and immune response durability. If successful, the vaccine could become available to the public by the late 2020s, pending regulatory review.

Public health experts emphasize that even with a successful vaccine, integrated prevention strategies will remain essential. “A vaccine would be a powerful tool, but it won’t replace the need for tick awareness and environmental management,” said Dr. Paul Mead, former chief of the CDC’s Lyme disease program. “We’ll still need to reduce tick habitats, educate the public, and promote early diagnosis and treatment.”

Other investigational approaches are also being explored. Researchers at Yale University are developing a vaccine that targets tick saliva proteins, aiming to provoke an immune response that makes it harder for ticks to feed successfully—a strategy known as anti-tick vaccination. Meanwhile, monoclonal antibody therapies designed to offer seasonal protection are in preclinical development, though none have yet reached human trials.

As climate change expands the geographic range of tick populations and lengthens their active season, the public health burden of Lyme disease continues to grow. The advancement of VLA15 represents a significant step toward reducing that burden through immunization, offering hope for a future where Lyme disease is far less common—and far less feared.