Lyme disease vaccine shows promise but narrowly misses its phase 3 target

So close, yet so far — The investigational LB6V Lyme disease vaccine, co-developed by Pfizer and Valneva, showed 73.2% efficacy in a phase 3 trial but narrowly missed its primary endpoint: the lower bound of the 95% confidence interval fell just below the required 20% threshold. A modified intent-to-treat analysis nudged the efficacy to 74.8% and cleared the bar. Researcher Paul Auwaerter, MD, of Johns Hopkins, called the results "clinically meaningful" and said the vaccine has real potential to reduce the Lyme disease burden.

The VALOR trial enrolled ~9,400 participants aged 5 and older across the U.S., Canada, and five European countries over three Lyme disease seasons (2022–2025). The vaccine targets six serotypes of the four most common Borrelia species in North America and Europe. One notable concern: efficacy dropped sharply from 73.2% in season two to just 18.6% in season three, suggesting annual boosters will likely be necessary. Pfizer has said it plans to seek regulatory approval, with a potential U.S. and European launch targeted for the second half of 2027.

By the Numbers:

• 73.2% vaccine efficacy in the evaluable population (95% CI 15.8–93.5%) — just missed the threshold
• 74.8% efficacy in the modified intent-to-treat analysis (95% CI 21.7–93.9%) — cleared the threshold
• ~476,000 people treated for Lyme disease annually in the U.S.; 80,000+ cases reported to the CDC each year
• Efficacy fell from 73.2% (season 2) to 18.6% (season 3), signaling the likely need for annual boosters

Why it matters: There's been no commercially available Lyme disease vaccine since LYMErix was pulled from the market in 2002. With cases on the rise, LB6V represents the most advanced candidate in over two decades — and despite the statistical stumble, experts believe it could still reach patients if regulators find the data compelling enough.