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Study on the Effectiveness of High-Dose vs. Standard-Dose Quadrivalent Influenza Vaccine in Preventing Flu in Adults Aged 65-79 in Galicia, Spain

Registered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial is focused on the prevention of influenza infection in adults aged 65 to 79 years. The study compares two types of flu vaccines: a high-dose quadrivalent influenza vaccine, known as Efluelda, and a standard-dose quadrivalent influenza vaccine, called Influvac Tetra. Both vaccines are designed to protect against four different strains of the flu virus, which include specific types like the B/Phuket/3073/2013-like virus and the A/Victoria/2570/2019 (H1N1)pdm09-like strain.

The purpose of the study is to evaluate how effective the high-dose vaccine is compared to the standard-dose vaccine in reducing the risk of hospitalization due to flu or pneumonia in the specified age group. Participants in the study will receive one of the two vaccines through an injection into the muscle. The study will monitor the health of participants to see if there is a difference in the number of hospitalizations for flu or pneumonia between the two groups.

Throughout the study, researchers will also look at other health outcomes, such as hospitalizations for any heart or lung-related diseases, overall hospitalizations, and overall mortality. The study aims to provide valuable information on which vaccine might offer better protection for older adults against serious flu-related complications.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Joining the study

    Upon joining the study, the participant will have already signed and dated an informed consent form. This confirms understanding and agreement to participate in the trial.

  2. Step 2

    Receiving the vaccine

    Participants will be randomly assigned to receive either a high-dose quadrivalent influenza vaccine (QIV-HD) or a standard-dose quadrivalent influenza vaccine (QIV-SD). The vaccine is administered as an intramuscular injection, which means it is given as a shot into a muscle.

    The vaccine is provided in a pre-filled syringe and is a suspension for injection. The high-dose vaccine contains 60 micrograms of hemagglutinin (HA) per strain, which is a component of the influenza virus used to help the body build protection against the flu.

  3. Step 3

    Monitoring period

    After receiving the vaccine, participants will be monitored for any immediate reactions to the injection. This is a standard procedure to ensure safety and well-being.

    Participants will be observed over the course of the study to evaluate the effectiveness of the vaccine in preventing hospitalization due to influenza or pneumonia.

  4. Step 4

    Follow-up and data collection

    Throughout the study, participants may be contacted for follow-up to collect data on health outcomes. This includes monitoring for any hospitalizations related to influenza, pneumonia, or other cardio-respiratory diseases.

    The study aims to assess the primary endpoint, which is the occurrence of hospitalization due to influenza or pneumonia. Secondary endpoints include hospitalization for any cardio-respiratory disease, all-cause hospitalization, all-cause mortality, and specific hospitalizations for influenza or pneumonia.

  5. Step 5

    End of study

    The estimated end date for the study is August 31, 2025. At the conclusion of the study, data will be analyzed to determine the relative effectiveness of the high-dose versus standard-dose vaccines in preventing hospitalizations.

Who can join the trial?

3 criteria

  • Must be between the ages of 65 and 79 years.
  • Must live in the community and not be eligible to receive the high-dose flu vaccine (QIV-HD) as part of regular care.
  • Must have signed and dated an informed consent form. This means you agree to participate in the study after being told about the details and risks.

Who cannot join the trial?

3 criteria

  • Participants must be between the ages of 65 and 79 years old.
  • Both men and women can participate.
  • Participants should not be part of a vulnerable population. A vulnerable population includes groups like pregnant women, children, or people who cannot make decisions for themselves.
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Investigated drugs

Quadrivalent Influenza Vaccine is a type of flu vaccine designed to protect against four different flu viruses. In this clinical trial, the vaccine is being tested in two forms: a high-dose version and a standard-dose version. The goal is to see which version is more effective in preventing serious flu-related illnesses, like hospitalization due to influenza or pneumonia, in older adults aged 65 to 79 years. The vaccine works by stimulating the body's immune system to recognize and fight the flu virus, helping to reduce the risk of getting sick.

What is already known about the treatment

  • High-Dose Quadrivalent Influenza Vaccine

    This vaccine is administered as an injection, typically into the muscle of the upper arm. It is currently used in medical practice to help prevent influenza infection, particularly in adults aged 65 to 79 years. The main purpose of this vaccine is to stimulate the immune system to produce antibodies that can fight off the influenza virus, thereby reducing the risk of severe illness and hospitalization. It is classified as a vaccine, which is a type of preventive medicine designed to protect against infectious diseases.

  • Standard-Dose Quadrivalent Influenza Vaccine

    This vaccine is also given as an injection into the muscle of the upper arm. It is widely used in healthcare to prevent influenza infection in various age groups, including older adults. The vaccine works by prompting the body's immune system to create antibodies that target the influenza virus, helping to prevent infection and reduce the severity of symptoms. Like the high-dose version, it is classified as a vaccine and serves as a preventive measure against the flu.

Investigated diseases

  • Influenza

    Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses. It primarily affects the nose, throat, and sometimes the lungs. The disease typically begins suddenly and can cause symptoms such as fever, cough, sore throat, muscle aches, and fatigue. Influenza spreads through droplets when an infected person coughs, sneezes, or talks. The virus can also be contracted by touching surfaces contaminated with the virus and then touching the face. The illness can range from mild to severe and can lead to complications, especially in older adults and those with weakened immune systems.

  • Pneumonia

    Pneumonia is an infection that inflames the air sacs in one or both lungs, which may fill with fluid or pus. It can be caused by bacteria, viruses, or fungi. Symptoms often include cough with phlegm or pus, fever, chills, and difficulty breathing. The disease can vary in severity from mild to life-threatening, with the severity often depending on the type of germ causing the infection, as well as the age and overall health of the individual. Pneumonia is spread through airborne droplets from a cough or sneeze, or by touching contaminated surfaces. It is more common in older adults, infants, and those with other health problems.

Trial detailsLast updated 7 Oct 2026
Age65+ yearsPhasePhase IIITrial ID2023-506977-36-00Protocol codeGALFLUEstimated enrolment114 011 patientsSponsorComplexo Hospitalario Universitario De Santiago

sourced from the EU Clinical Trials Register and site verification

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