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The LB6V Lyme disease vaccine candidate showed 73.2% efficacy in the trial’s evaluable population, but its confidence interval missed the prespecified success threshold. A modified intent-to-treat analysis showed 74.8% efficacy and narrowly cleared that threshold. Protection also appeared to wane by the third season, and no Lyme disease vaccine is currently available in the United States.
The investigational LB6V Lyme disease vaccine showed 73.2% efficacy in a phase III trial but missed its prespecified statistical success threshold in the evaluable population, according to results reported at the IDWeek meeting. A modified intent-to-treat analysis produced a 74.8% efficacy estimate that narrowly cleared the threshold, leaving the trial’s primary result short of its defined standard while suggesting the vaccine may reduce infections.
Among participants aged 5 and older in the evaluable population, Lyme disease was diagnosed in four people who received four doses of LB6V and 15 who received placebo. The resulting efficacy estimate was 73.2%, with a 95% confidence interval of 15.8% to 93.5%. The trial’s predefined success criterion required the lower bound of that interval to exceed 20%; it did not.
In a modified intent-to-treat analysis, the efficacy estimate was 74.8%, with a 95% confidence interval of 21.7% to 93.9%, which just exceeded the same lower-bound criterion. Paul Auwaerter, MD, of Johns Hopkins University School of Medicine presented the results. The two analyses use different participant groupings, so the modified analysis does not change the fact that the evaluable-population result failed the stated threshold.
The placebo-controlled VALOR trial enrolled about 9,400 people at elevated risk in the United States, Canada and five European countries. Participants received vaccine or placebo at baseline, two months, about five to nine months, and around 18 months. The primary efficacy assessment covered the period beginning 28 days after dose four through the end of the Lyme disease season.
What the Trial Result Means
The findings offer a possible route toward prevention of a disease for which no vaccine is currently available in the United States, but they do not amount to an unambiguous phase III success under the trial’s prespecified primary analysis. The confidence intervals are wide, reflecting uncertainty around the efficacy estimates; the lower bound in the evaluable group falls below the required threshold even though the point estimate is above 70%.
The trial also found that the estimated efficacy fell to 18.6% in the third season after vaccination, with a very wide 95% confidence interval of -220.0% to 80.4%. The report said antibody levels declined over the same period. This pattern raises questions about how long protection lasts and whether additional doses would be needed, but the trial results as provided do not establish a booster schedule.
Safety findings are also relevant to future evaluation. Adverse events were reported in 58.8% of vaccine recipients and 52.6% of placebo recipients. Fatigue, headache, muscle and joint pain, as well as injection-site pain, redness and swelling, were more common in vaccine recipients. Treatment-related adverse events that led to withdrawal occurred in 0.3% of vaccine recipients and 0.1% of placebo recipients; newly diagnosed chronic medical conditions were reported at similar rates in the two groups.
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How LB6V Was Tested
LB6V, previously known as VLA15, is an adjuvanted protein-subunit vaccine designed to target six serotypes across four Borrelia species common in Europe and North America. The proposed mechanism is that vaccinated people pass antibodies to ticks during a bite; those antibodies are intended to inhibit Borrelia burgdorferi in the tick and prevent transmission to the person.
The trial ran across three Lyme disease seasons from 2022 to 2025. Participants were considered at increased risk because of factors such as occupation, home environment or leisure activities. The median age was 47, 52% were female, and 97% had at least two recorded Lyme disease risk factors, according to the reported trial description.
Lyme disease is caused by infection with Borrelia bacteria carried by blacklegged ticks. Symptoms can include fever, headache, fatigue and erythema migrans, a characteristic expanding rash; untreated infection can affect joints, the heart and the nervous system. The report cited more than 80,000 cases reported to the CDC annually in the United States and an estimated 476,000 people treated each year. A prior Lyme vaccine, LYMErix, was approved in 1998 and withdrawn by its manufacturer in 2002 amid concerns about side effects and declining sales.
“Overall, I do think this vaccine has the potential to lower the Lyme disease burden.”
— Paul Auwaerter, MD, Johns Hopkins University School of Medicine
Questions About Durability and Approval
The reported results do not establish whether regulators will consider the modified intent-to-treat analysis sufficient despite the evaluable-population analysis missing its prespecified threshold. The source material does not state what regulatory submission, review or decision is planned, or provide a timeline for one.
Protection beyond the observed trial seasons remains uncertain. The third-season efficacy estimate had a particularly wide confidence interval, and the supplied report does not specify how long protection might last after a booster or whether a revised dosing schedule could improve durability. The results also do not establish how well the vaccine would perform in populations beyond the trial’s elevated-risk participants.
Next Steps for LB6V
Further evaluation will need to address the discrepancy between the two efficacy analyses and the apparent decline in protection over time. Auwaerter said the antibody findings may support future immunobridging studies, which use immune-response measures to help assess protection, but the report does not say whether such studies have begun or what their design would be.
Any next steps in the vaccine’s development, including a possible booster strategy or regulatory review, remain unconfirmed in the available report. For now, LB6V remains an investigational candidate, and the trial results do not change the current absence of an available Lyme disease vaccine in the United States.
Key Questions
Did LB6V meet the phase III trial’s success threshold?
Not in the evaluable-population analysis. Its 73.2% efficacy estimate had a 95% confidence interval with a 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%, narrowly clearing that criterion.
How many Lyme disease cases were reported in the evaluable group?
Four participants who received four LB6V doses developed Lyme disease, compared with 15 participants who received placebo.
Did the vaccine’s protection last across all three seasons?
The reported efficacy estimate fell from 73.2% in the second season after the four-dose vaccination to 18.6% in the third season. The third-season confidence interval was very wide, so the estimate leaves substantial uncertainty about protection.
Is LB6V approved or available to the public?
No. The supplied report describes LB6V as an investigational vaccine candidate and says there are no currently available Lyme disease vaccines in the United States.
Did the trial identify a recommended annual booster?
No booster schedule was established in the reported results. Auwaerter said an annual booster before Lyme disease season would make sense, but that was his view, not a confirmed dosing recommendation or regulatory decision.
Source: medpagetoday.com
