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The investigational Lyme disease vaccine LB6V reduced cases in a phase III trial, but its primary analysis did not meet the trial’s preset statistical success threshold. A modified intent-to-treat analysis narrowly cleared that threshold, while protection appeared to wane by the third season after vaccination.
An investigational Lyme disease vaccine reduced infections in a large phase III trial but missed its prespecified success threshold in the primary analysis, according to results presented at the IDWeek annual meeting. A modified intent-to-treat analysis narrowly met the threshold, leaving the trial’s statistical outcome dependent on which analysis population is considered.
Among participants aged 5 and older in the evaluable population, four LB6V recipients developed Lyme disease, compared with 15 given placebo. That produced an estimated vaccine efficacy of 73.2%, with a 95% confidence interval of 15.8% to 93.5%. The trial required the confidence interval’s lower bound to exceed 20%; it did not in this analysis.
In a modified intent-to-treat analysis, estimated efficacy was 74.8% (95% CI 21.7% to 93.9%), just above the prespecified lower-bound requirement. Paul Auwaerter, MD, of Johns Hopkins University School of Medicine, presented the results. The distinction matters: the alternative analysis cleared the stated statistical cutoff, but it does not change the primary analysis’s miss.
The randomized, placebo-controlled VALOR trial enrolled about 9,400 people at elevated risk because of their work, home environment or leisure activities. Participants received four doses of vaccine or placebo, and researchers followed them across three Lyme disease seasons from 2022 through 2025. The primary endpoint measured efficacy from 28 days after dose four through the end of the Lyme disease season.
A Possible Vaccine, With a Statistical Caveat
Lyme disease is transmitted by infected blacklegged ticks and can cause fever, headache, fatigue and a characteristic expanding rash. If untreated, infection can spread to the joints, heart and nervous system. The report says more than 80,000 cases are reported annually to the U.S. Centers for Disease Control and Prevention, while an estimated 476,000 people are treated each year.
There is currently no Lyme disease vaccine available. LB6V’s results suggest it may reduce illness, but the primary analysis did not satisfy the trial’s preset criterion. The gap between the two analyses, alongside wide confidence intervals, means the findings should not be read as a conclusive measure of how well the vaccine protects across all groups or seasons.
Safety findings also inform the picture. Adverse events were reported by 58.8% of vaccine recipients and 52.6% of placebo recipients. Fatigue, headache, muscle and joint pain, and injection-site reactions were more common in vaccine recipients. Treatment-related events that led to withdrawal occurred in 0.3% and 0.1%, respectively; newly diagnosed chronic conditions were reported at similar rates.
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Four Doses and Waning Protection
LB6V, previously called VLA15, is an adjuvanted protein-subunit vaccine designed to target six serotypes across four Borrelia species common in Europe and North America. The trial’s vaccination schedule was at baseline, two months, about five to nine months, and around 18 months. The study included sites in five European countries, Canada and the United States.
The vaccine’s estimated efficacy fell from 73.2% in the second season after the four-dose series to 18.6% in the third season. The third-season estimate had a very wide confidence interval, from -220.0% to 80.4%, so it is highly uncertain. Antibody levels against Borrelia burgdorferi outer surface protein A serotype 1 also declined, from geometric mean titers of 1,100.3 to 35.7 across those seasons.
Auwaerter said the trial’s findings point to a possible relationship between antibody levels and disease risk, but the results do not establish a booster schedule. An earlier Lyme vaccine, LYMErix, was approved by the FDA in 1998 and withdrawn by its manufacturer in 2002 amid side-effect concerns and declining sales, according to the report.
“Overall, I do think this vaccine has the potential to lower the Lyme disease burden.”
— Paul Auwaerter, MD, of Johns Hopkins University School of Medicine
The Meaning of the Trial’s Two Analyses
The primary analysis did not meet the preset criterion, while the modified intent-to-treat analysis did so narrowly. The supplied report does not detail why the analysis populations produced different outcomes or provide enough information to assess the impact of that difference. The confidence intervals are broad, reflecting uncertainty around the efficacy estimates.
It is also unclear whether the third-season decline reflects waning protection, the small number of cases, or other factors; the wide interval makes the estimate particularly imprecise. The report does not specify the sponsor’s regulatory plans, whether further analyses are planned, or whether a booster-dose regimen will be tested. The trial findings alone do not establish that the vaccine is approved or available.
Further Analyses and Booster Plans
The next questions are whether the trial results will be published with full methods and subgroup data, and how the investigators or sponsor will address the difference between the primary and modified analyses. The source report does not give a timeline for those steps or announce a regulatory decision.
Researchers may also examine whether antibody measurements can help predict protection and guide future studies, as Auwaerter suggested. Any annual booster approach would need further evaluation; no booster schedule was established by the results described. Until additional evidence or regulatory updates emerge, LB6V remains an investigational candidate rather than an available Lyme disease vaccine.
Key Questions
Did LB6V meet the phase III trial’s success threshold?
Not in the primary evaluable-population analysis. Its 73.2% efficacy estimate had a 95% confidence interval lower bound of 15.8%, below the required level of more than 20%. A modified intent-to-treat analysis estimated 74.8% efficacy, with a lower bound of 21.7%, and narrowly cleared the criterion.
How many Lyme disease cases occurred in the primary analysis?
Four vaccine recipients and 15 placebo recipients developed Lyme disease in the evaluable population aged 5 and older.
Did protection remain steady across the trial?
No. The reported efficacy estimate fell from 73.2% in the second season after the four-dose series to 18.6% in the third. The third-season confidence interval was extremely wide, so that estimate is uncertain.
Is LB6V available to the public?
The supplied report describes LB6V as an investigational vaccine candidate and does not report approval or availability. It says no Lyme disease vaccine is currently available.
Source: rss
