Six-strain Lyme vaccine shows promise for children after two-decade US gap

A four-dose investigational vaccine was well tolerated in a phase 3 trial of more than 3,500 children and teenagers, as developers prepare to seek US approval.

A four-dose investigational Lyme disease vaccine appears to be safe and generally well tolerated in children and teenagers, according to results from a phase 3 trial presented at the American Academy of Pediatrics’ annual conference in San Diego. The findings add to growing evidence that a new vaccine could eventually help protect children, who are among the age groups at highest risk of Lyme disease in the United States.

The study evaluated LB6V, previously known as VLA15, in 3,547 healthy participants aged 5 to 17 years at 57 sites across the United States between December 2022 and July 2025. Researchers assigned children and adolescents to receive either the vaccine or placebo in a four-dose schedule. Most side effects were mild to moderate, with injection-site pain and redness, fatigue and headache among the most common complaints. Serious adverse events were uncommon and occurred at similar rates in the vaccine and placebo groups.

Kristopher Paolino and colleagues reported that only a small proportion of adverse events were considered related to the vaccine. Fever and local reactions were somewhat more common in younger children than in teenagers, but severe fever was rare and other serious systemic reactions were not seen. One death occurred in the placebo group and was judged unrelated to the study treatment. The trial also showed high completion rates in both age groups, suggesting the schedule was feasible for families who stayed in the study.

Pfizer and Valneva said in separate statements that the broader phase 3 VALOR trial found more than 70% efficacy in preventing Lyme disease in people aged 5 and older. The companies said the vaccine was well tolerated and that they plan to seek regulatory approval. The Centres for Disease Control and Prevention says there is currently no licensed Lyme disease vaccine in the United States, and that the only earlier product, LYMErix, was withdrawn in 2002 after weak demand, despite initial approval in 1998. If LB6V is approved, it would be the first human Lyme vaccine available in more than two decades.

The new candidate differs from LYMErix in important ways. Like its predecessor, it targets OspA, a surface protein on the bacterium Borrelia burgdorferi, which causes Lyme disease and is spread by black-legged ticks. But LB6V contains six OspA serotypes, rather than one, which is intended to make it more broadly useful across regions in North America and Europe. Experts quoted in the Medscape report also said the newer design was intended to address old concerns about possible autoimmune effects that dogged LYMErix, although later research did not support that theory. Even so, any future rollout is likely to depend not only on regulatory approval but also on a clear recommendation from the Advisory Committee on Immunization Practices, which could help determine insurance coverage and public confidence.