Pfizer announced on Monday that it will move forward with seeking regulatory approval for its Lyme disease vaccine candidate, even though the shot did not meet the primary endpoint in a late-stage clinical trial.
According to the company, the trial fell short of its statistical target because too few participants actually contracted Lyme disease during the study, making it difficult to generate definitive results. However, Pfizer emphasized that the vaccine still demonstrated strong performance, reducing infection rates by more than 70% compared to a placebo — a level of efficacy the company believes is sufficient to present to regulators.
“The efficacy shown in the VALOR study of more than 70% is highly encouraging and creates confidence in the vaccine’s potential to protect against this disease that can be debilitating,” Pfizer Chief Vaccines Officer Annaliesa Anderson said in a statement.
The Lyme disease vaccine is not expected to become a major revenue driver for Pfizer. Its partner, Valneva, has projected peak annual sales of around $1 billion. In comparison, Pfizer anticipates total revenue of approximately $60 billion this year, with its COVID-19 vaccine alone contributing over $5 billion.
Still, the Lyme vaccine had been positioned as a key growth opportunity for the company in 2026, offering the potential to introduce the first widely available human vaccine for Lyme disease.
Pursuing approval for a vaccine that technically failed a clinical trial could present regulatory challenges, particularly in a climate where stricter oversight of vaccines is being emphasized. The decision may also serve as a broader test case for U.S. vaccine policy going forward.
Lyme disease is a bacterial infection typically transmitted to humans through tick bites. It can lead to serious symptoms such as arthritis, muscle weakness, and chronic pain. Each year, roughly 500,000 Americans are diagnosed with or treated for Lyme disease, according to estimates from the Centers for Disease Control and Prevention.
Despite its widespread impact — particularly in the northeastern United States — there is currently no approved vaccine for humans. A previous attempt by a company that later became GSK introduced a vaccine called LYMErix in 1998, but it was withdrawn just a few years later due to declining demand driven by safety concerns. That setback slowed progress in human Lyme vaccine development, even as vaccines for dogs became more common.
Pfizer and Valneva have also faced hurdles during development. In 2023, they removed roughly half of the participants from their Phase 3 trial due to quality concerns linked to third-party trial operator Care Access. The study initially enrolled around 18,000 participants but was reduced to approximately 9,400 after those adjustments.
The vaccine works by targeting outer surface protein A found on the bacteria responsible for Lyme disease. Once vaccinated, the human body produces antibodies that can transfer to ticks during a bite, preventing the bacteria from being transmitted. The vaccination schedule includes three doses in the first year, followed by a booster shot the next year.
Pfizer and Valneva reported that no safety issues were identified during the trial.
