Evaluation of Immunogenicity of Co-Administered Tozinameran and MF59-Adjuvanted Influenza Vaccine in Adults Aged 65 and Over with COVID-19 and Influenza

The primary objective of this clinical trial is to assess the **humoral immune response** elicited by a licensed COVID-19 vaccine when co-administered with a licensed MF59 adjuvanted seasonal influenza vaccine in adults aged 65 years and over. This is compared to the immune response from a licensed COVID-19 vaccine co-administered with an unadjuvanted seasonal influenza vaccine or the COVID-19 vaccine alone. Evaluating the humoral immune response is clinically relevant as it provides insights into the effectiveness of vaccine combinations in enhancing immunity against COVID-19 and influenza in older adults, a population at higher risk for severe outcomes from these infections.

Secondary objectives include: - Evaluating the **cellular immune response** elicited by the same vaccine combinations, which is crucial for understanding the broader immune protection offered by the vaccines. - Assessing the safety and **reactogenicity** of the licensed COVID-19 vaccine when co-administered with the licensed MF59 adjuvanted seasonal influenza vaccine, compared to the other vaccine combinations. This is important for determining the tolerability and potential side effects of these vaccine regimens in the elderly population.

The clinical trial involves **adults aged 65 years and over** who are being assessed for their humoral immune response to a licensed COVID-19 vaccine when co-administered with a licensed MF59 adjuvanted seasonal flu vaccine. The study population includes both **male and female** participants, and the trial does not focus on a vulnerable population. Participants were selected based on their willingness to provide written informed consent and their ability to comply with the trial protocol requirements. The sponsor has not provided information regarding the total number of participants. The trial does not specify any particular lifestyle considerations such as diet or physical activity. The study aims to compare the immune response elicited by the co-administration of the vaccines against the response from the COVID-19 vaccine alone or with an unadjuvanted seasonal flu vaccine.

The clinical trial is designed to evaluate the **immunogenicity** of a licensed COVID-19 vaccine when co-administered with a licensed MF59 adjuvanted seasonal influenza vaccine in adults aged 65 years and older. This is a multi-center, randomized, single-blind trial. Participants will be randomly assigned to receive either the COVID-19 vaccine with the adjuvanted influenza vaccine, the COVID-19 vaccine with an unadjuvanted influenza vaccine, or the COVID-19 vaccine alone. The trial aims to assess the humoral immune response, specifically the serum neutralizing antibody response to SARS-CoV-2 variants of concern, and the change in geometric mean titres of serum anti-SARS-CoV-2 spike glycoprotein specific binding antibody at various time points.

The trial will commence with a screening visit to confirm eligibility based on inclusion criteria, such as age and willingness to provide informed consent. Following successful screening, participants will be enrolled and receive their assigned vaccinations. Study visits are scheduled at days 0, 10, 28, and 90 to collect blood samples for immunogenicity assessments and to monitor safety and reactogenicity. The primary endpoints include the measurement of serum neutralizing antibody responses and the longevity of these responses. Secondary endpoints focus on cellular immunity characterization and the safety profile of the vaccines, including the frequency and severity of adverse events.

The expected duration of participant involvement is approximately 90 days, with the trial estimated to conclude by June 30, 2025. Participants may be withdrawn from the study if they experience serious adverse events or if they are unable to comply with the trial protocol requirements. The trial is not classified as low intervention and is categorized as a Phase 4 study, focusing on the population affected by COVID-19 and influenza. The trial's design ensures rigorous assessment of the vaccines' immunogenicity and safety in the target demographic.

The clinical trial involves the administration of several treatments, including both experimental and non-experimental medications. The **experimental medication** is the "Comirnaty 30 micrograms/dose concentrate for dispersion for injection COVID-19 mRNA Vaccine." This vaccine contains the active substance **tozinameran**, a nucleoside-modified mRNA encoding a modified version of the SARS-CoV-2 spike protein. The pharmaceutical form is a dispersion for injection, and it is administered as a single 0.5 ml intramuscular injection. The dosing schedule is a single administration, and participant compliance is monitored through standard clinical trial procedures.

The trial also includes the administration of "Influvac sub-unit Tetra," a suspension for injection in a pre-filled syringe. This **influenza vaccine** contains surface antigens from inactivated strains, including B/Phuket/3073/2013-like virus, Influenza virus A/Darwin/9/2021 SAN-010 (H3N2), Influenza virus B/Austria/1359417/2021-like strain, and Influenza A/Victoria/4897/2022 IVR-238 (H1N1). The vaccine is administered as a single 0.5 ml intramuscular injection. The dosing schedule is a single administration, and compliance is monitored as per trial protocols.

Another treatment used in the trial is "Fluad Tetra," a suspension for injection in a pre-filled syringe. This is an **adjuvanted influenza vaccine** containing surface antigens from inactivated strains, including B/Phuket/3073/2013-like strain, Influenza virus B/Austria/1359417/2021-like strain, A/Darwin/9/2021 (H3N2)-like strain, and A/Victoria/4897/2022 (H1N1)pdm09-like strain. The vaccine is administered as a single 0.5 ml intramuscular injection. The dosing schedule is a single administration, with compliance monitored according to the study protocol.

The non-experimental treatment in this trial is a **saline injection** used as a placebo comparator. This is a 0.5 ml NaCl 0.9% solution administered as a single-shot intramuscular injection. The placebo is used to assess the immunogenicity of the experimental and comparator vaccines, ensuring that any observed effects are due to the active treatments rather than psychological or other non-specific effects. Compliance with the placebo administration is monitored in line with the trial's standard procedures.

Efficacy in this clinical trial will be assessed through a series of primary and secondary endpoints designed to evaluate the immune response and safety of co-administered vaccines. The primary endpoints focus on the **serum neutralizing antibody response** to SARS-CoV-2 variants of concern (VOCs) at specific timepoints: days 0, 10, and 28. Additionally, the change in geometric mean titres (GMT) of serum anti-SARS-CoV-2 spike glycoprotein specific binding antibody will be measured at days 10 and 28, relative to baseline measurements on day 0. The longevity of humoral responses will also be assessed by measuring the serum neutralizing and binding antibody responses to SARS-CoV-2 VOCs at day 90.

Secondary endpoints include the characterization of cellular immunity, specifically antigen-specific cytotoxic T cells (CTL), T helper cells (Th) responses, and T cell memory, using ELISpot and/or intracellular cytokine staining (Flow cytometry) at days 0 and 28. The longevity of cellular immune responses will be evaluated on day 90. Safety and reactogenicity will be monitored by recording the frequency and severity of solicited local and systemic adverse events (AEs) within 7 days of vaccination, all unsolicited AEs within 28 days, and all serious adverse events (SAEs) from day 0 until day 90 or the end of the trial.