Phase 3 Multicenter Randomized Placebo-Controlled Trial Evaluating Efficacy, Safety, and Immunogenicity of VLA15 Vaccine for Lyme Disease in Individuals Aged ≥5 Years

The primary objective of this Phase 3, multicenter, placebo-controlled, randomized, observer-blinded trial is to evaluate the **efficacy** of VLA15 in preventing confirmed Lyme disease during the Lyme disease season following the completion of the primary series vaccination and booster dose. This is clinically relevant as Lyme disease is a significant public health concern, and effective vaccination could substantially reduce the incidence of this tick-borne illness. Additionally, the trial aims to describe the **safety** profile of VLA15 by assessing the percentage of participants reporting local reactions, systemic events, adverse events (AEs), non-disabling clinically meaningful conditions (NDCMCs), and serious adverse events (SAEs). Furthermore, the trial seeks to demonstrate that the **immunogenicity** of VLA15, as measured by immune responses to the six serotypes, is consistent across three independent lots and that the immune responses in children aged 5-17 years are noninferior to those in adults aged 18-44 years after the booster dose.

Secondary objectives include:

• Demonstrating the efficacy of VLA15 in preventing confirmed Lyme disease during the Lyme disease season after completion of the primary series vaccination and booster dose in North America.
• Demonstrating the efficacy of VLA15 in preventing confirmed Lyme disease during the Lyme disease season after completion of the primary series vaccination.

The clinical trial for the **active immunization against Lyme disease** involves a total of 6,400 participants. The study population includes both male and female subjects, with an age range starting from 5 years and above, depending on the country's regulations regarding pediatric enrollment. Participants are selected based on their residence in areas where Lyme disease is endemic and their engagement in lifestyles that increase their risk of exposure to the disease. This includes individuals involved in outdoor occupations or recreational activities such as hiking, camping, and gardening in tick-infested areas. The trial includes healthy individuals, as determined by medical history and clinical judgment, although those with stable preexisting chronic medical conditions may also be eligible. Participants are required to be capable of providing informed consent and must be willing to comply with all study procedures and visits. The trial population is diverse, encompassing both genders and including vulnerable populations, ensuring a comprehensive assessment of the vaccine's efficacy and safety across different demographic groups.

The clinical trial is a **Phase 3**, multicenter, placebo-controlled, randomized, observer-blinded study designed to evaluate the efficacy, safety, tolerability, immunogenicity, and lot consistency of a 6-valent OspA-based vaccine for active immunization against **Lyme disease**. The trial involves healthy participants aged 5 years and older, residing in areas endemic to Lyme disease, who are at increased risk due to their lifestyle or occupation. The study is expected to run from August 2022 to December 2025, with participant involvement lasting up to four years, including the primary series vaccination and booster dose.

The trial design includes a screening visit to assess eligibility based on inclusion criteria such as age, health status, and risk factors for Lyme disease. Participants will be randomly assigned to receive either the investigational vaccine, VLA15, or a placebo, which is a **sodium chloride solution 0.9%**. The trial is double-blind, meaning neither the participants nor the investigators will know which treatment is being administered, to ensure unbiased results.

Study visits are scheduled to monitor the participants' health and collect data on the vaccine's efficacy and safety. These visits include follow-up assessments to record any local reactions, systemic events, adverse events (AEs), non-drug-related clinically meaningful conditions (NDCMCs), and serious adverse events (SAEs). Immunogenicity will be evaluated through anti-OspA quantitative immunological assays to ensure the immune response is consistent across different lots and age groups.

The end-of-study visit will conclude the trial for each participant, where final assessments will be conducted to gather comprehensive data on the vaccine's long-term effects. Participants may be withdrawn from the study early if they experience significant adverse reactions, fail to comply with study procedures, or if the investigator deems it necessary for their safety. The trial aims to provide robust data to support the vaccine's efficacy and safety profile, contributing to the prevention of Lyme disease in at-risk populations.

The clinical trial involves the administration of two treatments: **VLA15** and **Sodium Chloride Solution 0.9%**. **VLA15** is an investigational vaccine designed to prevent Lyme disease. It is formulated as a **suspension for injection in a pre-filled syringe**. The active substances in VLA15 include a combination of outer surface protein A (OspA) from six different serotypes of **Borrelia burgdorferi**, the bacterium responsible for Lyme disease. These proteins are fused via linkers to enhance immunogenicity. The vaccine is administered via **intramuscular injection**. The dosing schedule includes a primary series followed by a booster dose, with a maximum daily dose of 0.5 ml and a total dose not exceeding 2 ml over a treatment period of 4 months. Participant compliance is monitored through scheduled visits and documentation of vaccine administration.

**Sodium Chloride Solution 0.9%**, commonly known as normal saline, serves as the placebo in this trial. It is a **solution for injection** and is administered via **intramuscular injection**. The solution is chemically composed of sodium chloride dissolved in water, providing isotonicity with human plasma. The dosing regimen for the placebo mirrors that of the experimental vaccine, with a maximum daily dose of 0.5 ml and a total dose not exceeding 2 ml over a 4-month period. Compliance with the placebo administration is similarly monitored through scheduled visits and documentation.

The efficacy of the VLA15 vaccine in preventing **Lyme disease** will be assessed through a Phase 3, multicenter, placebo-controlled, randomized, observer-blinded clinical trial. The primary efficacy endpoint is the prevention of clinically and laboratory-confirmed Lyme disease caused by *Borrelia burgdorferi* sensu lato. This will be determined by an adjudication committee (AC) during the Lyme disease season following the completion of the primary series vaccination and booster dose.

To evaluate the primary immunogenicity, the trial will measure the anti-OspA quantitative immunological assay titer. This will assess the immune responses to the six serotypes induced by VLA15, ensuring they are equivalent across three independent lots. Additionally, the immune responses in children aged 5-17 years will be compared to those in adults aged 18-44 years to confirm noninferiority after the booster dose.

The collection and analysis of efficacy data will be conducted at specified timepoints throughout the trial, with the primary focus on the period following the booster dose. The trial is designed to ensure rigorous assessment of the vaccine's efficacy in a population at increased risk for Lyme disease, including individuals residing in endemic areas and those with lifestyles that increase exposure risk.