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The investigational Lyme disease vaccine LB6V did not meet the phase III trial’s prespecified success threshold in the primary evaluable-population analysis, despite an estimated efficacy of 73.2%. A modified intent-to-treat analysis produced an estimate of 74.8% and narrowly cleared the threshold, while efficacy fell in the third season after vaccination.
An investigational Lyme disease vaccine, LB6V, narrowly missed its prespecified success threshold in a phase III trial, even though researchers estimated efficacy at 73.2% in the primary evaluable-population analysis. A modified intent-to-treat analysis showed 74.8% efficacy and just cleared the threshold, leaving the candidate’s results dependent on which analysis is used.
Among participants aged 5 and older in the evaluable population, four LB6V recipients developed Lyme disease, compared with 15 people given placebo. The resulting vaccine efficacy estimate was 73.2%, with a 95% confidence interval of 15.8% to 93.5%. The trial’s predefined success rule required the lower end of that interval to be greater than 20%, so the primary result did not meet the criterion.
In the modified intent-to-treat analysis, the estimated efficacy was 74.8%, with a 95% confidence interval of 21.7% to 93.9%. That lower confidence bound was above the 20% threshold. Paul Auwaerter, MD, of Johns Hopkins University School of Medicine, presented the results at the IDWeek annual meeting. The report does not establish that regulators have accepted this analysis as sufficient for approval.
The trial, called VALOR, enrolled about 9,400 people at increased risk in the United States, Canada and five European countries. Participants received four doses of vaccine or placebo, with the primary efficacy window beginning 28 days after dose four. The study ran across three Lyme disease seasons, from 2022 to 2025. Reported adverse events occurred in 58.8% of vaccine recipients and 52.6% of placebo recipients; events that led to withdrawal and were considered treatment-related occurred in 0.3% and 0.1%, respectively.
A Potential Vaccine With a Statistical Caveat
The results matter because no Lyme disease vaccine is currently available for people in the United States, despite the disease’s substantial reported burden. The source report says more than 80,000 cases are reported to the CDC annually and estimates that 476,000 people are treated each year. Those figures describe different measures: reported cases and estimated treatment volume.
LB6V’s results offer evidence of possible protection, but the missed primary threshold complicates conclusions about whether the trial demonstrated success under its prespecified standard. The modified analysis is encouraging, but it does not erase the primary result. The findings also raise a practical question about durability: efficacy was estimated at 18.6% in the third season, down from 73.2% in the second. That third-season estimate had a very wide confidence interval, from -220.0% to 80.4%, so it is highly uncertain.
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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 feeding ticks; those antibodies act against Borrelia bacteria in the tick and may prevent transmission.
Participants received doses at baseline, two months, about five to nine months, and about 18 months. The trial population had a median age of 47; 52% were female, and 97% had at least two Lyme disease risk factors. The source report says earlier phase II trials found the vaccine generated an immune response and appeared safe. The only previous Lyme vaccine approved in the United States, LYMErix, was approved in 1998 and withdrawn by its manufacturer in 2002 amid concerns about side effects 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, Johns Hopkins University School of Medicine, speaking at IDWeek
Durability and Approval Questions Remain
The trial report leaves several issues unresolved. It does not explain in detail why the modified intent-to-treat population differs from the evaluable population, or whether the study sponsor or regulators will treat that analysis as adequate evidence of efficacy. The primary endpoint missed its stated criterion, and the available account does not give a regulatory decision or an approval timeline.
The third-season efficacy estimate is also imprecise, with a confidence interval spanning a large range. Antibody levels against one measured B. burgdorferi protein fell from 1,100.3 to 35.7 between the second and third seasons, but the report does not establish how long protection lasts across all targeted serotypes. Vaccine recipients more often reported fatigue, headache, muscle and joint pain, and injection-site reactions; newly diagnosed chronic medical conditions were similar between groups, at 9.6% and 9.5%. Longer-term safety and the need for additional doses remain open questions.
Further Review and Booster Research
The next steps are not specified in the meeting report. The study results will need further review by researchers and, if the sponsor seeks authorization, by relevant regulators. Any decision will need to account for the primary analysis, the modified analysis, safety findings and the decline in estimated protection over time.
Auwaerter said the relationship between antibody levels and disease risk could support future immunobridging studies, which use immune-response measures to help assess protection. The data may also inform research into whether a booster before each Lyme season is warranted. For now, LB6V remains investigational; the trial findings do not establish that it is approved or that annual boosters are recommended.
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 lower 95% confidence bound of 15.8%, below the required level of greater than 20%. A modified intent-to-treat analysis had a 21.7% lower bound and narrowly met that statistical criterion.
How many Lyme disease cases occurred in the primary analysis?
Among participants in the evaluable population aged 5 and older, four vaccine recipients and 15 placebo recipients developed Lyme disease.
How long did the apparent protection last?
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 very wide, so the estimate is uncertain; the findings do not establish a precise duration of protection.
Is the Lyme vaccine available now?
No. LB6V is described as an investigational vaccine candidate, and the source report does not announce regulatory approval or availability.
Were side effects more common with LB6V?
Reported adverse events occurred in 58.8% of LB6V recipients and 52.6% of placebo recipients. Fatigue, headache, muscle and joint pain, and injection-site symptoms were more likely in vaccine recipients, while newly diagnosed chronic medical conditions occurred at similar rates in both groups.
Source: medpagetoday.com
