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Study Comparing High-Dose vs. Standard-Dose Influenza Vaccine for Preventing Flu in Older Adults

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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 studying the prevention of influenza infection in older adults. The study compares two types of vaccines: a high-dose quadrivalent influenza vaccine and a standard-dose quadrivalent influenza vaccine. Quadrivalent vaccines are designed to protect against four different strains of the influenza virus. The high-dose vaccine is intended to provide a stronger immune response, which may be particularly beneficial for older adults who are at higher risk of complications from influenza.

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 influenza or pneumonia. Pneumonia is a lung infection that can be a serious complication of influenza, especially in older adults. Participants in the study will receive either the high-dose or standard-dose vaccine through an intramuscular injection, which means the vaccine is given as a shot into a muscle.

Throughout the study, researchers will monitor participants to see if they are hospitalized for influenza, pneumonia, or any other cardio-respiratory diseases, which affect the heart and lungs. They will also track all-cause hospitalizations and mortality. The study aims to provide valuable information on which vaccine might offer better protection for older adults, ultimately helping to guide future vaccination strategies for this age group.

The research process

The trial runs in 4 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, 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). This is to evaluate the effectiveness of the two different doses in preventing influenza and related hospitalizations in older adults.

  2. Step 2

    Receiving the vaccine

    Participants will receive the assigned vaccine through an intramuscular injection. This means the vaccine will be injected into a muscle, typically in the upper arm. The vaccine is given as a single dose.

  3. Step 3

    Monitoring and follow-up

    After receiving the vaccine, participants will be monitored for any immediate reactions. Follow-up will continue throughout the influenza season to track any hospitalizations due to influenza or pneumonia, as well as other health outcomes.

    Participants will be asked to report any hospital visits or health changes during the study period. This information helps in assessing the effectiveness of the vaccine in preventing serious health issues.

  4. Step 4

    End of study

    The study is expected to conclude by August 31, 2025. At the end of the study, data collected will be analyzed to determine the relative effectiveness of the high-dose versus standard-dose vaccines in preventing hospitalizations and other health outcomes.

Who can join the trial?

3 criteria

  • Must be 65 years or older. Depending on government recommendations, the age range might be adjusted. For example, if the government decides to offer a specific vaccine only to those aged 80 and above, the study will focus on those aged 65-79 years.
  • Both men and women can participate.
  • Participants should not belong to a vulnerable population, meaning they should not have conditions that make them more susceptible to harm or exploitation.

Who cannot join the trial?

7 criteria

  • Participants must not have a known allergy to any component of the vaccine. An allergy is when your body reacts negatively to a substance.
  • Participants should not have had a severe reaction to a previous flu vaccine. A severe reaction means a strong negative response, like difficulty breathing or swelling.
  • Participants must not have a history of Guillain-Barré syndrome. Guillain-Barré syndrome is a rare condition where the body's immune system attacks the nerves.
  • Participants should not be currently participating in another clinical trial. A clinical trial is a research study to test new treatments.
  • Participants must not have a weakened immune system. A weakened immune system means your body has a harder time fighting infections.
  • Participants should not be pregnant. Pregnant means expecting a baby.
  • Participants must not have any other medical condition that the study doctors think would make it unsafe for them to participate.
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Investigated drugs

Quadrivalent Influenza Vaccine is a type of flu shot designed to protect against four different strains of the influenza virus. In this clinical trial, the vaccine is being tested in two different strengths to see which one is more effective in preventing serious illnesses like the flu and pneumonia in older adults. The goal is to find out if a higher dose of the vaccine offers better protection compared to the standard dose. This vaccine works by helping your body build up its defense system against the flu, reducing the chances of getting sick or needing to go to the hospital.

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 infections, particularly in older adults. The main purpose of this vaccine is to reduce the risk of hospitalization due to influenza or pneumonia. It works by stimulating the immune system to produce antibodies that can recognize and fight the influenza virus. This vaccine is classified as an immunization agent, specifically designed to protect against four different strains of the influenza virus.

  • 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 infections, especially in older adults. The primary goal of this vaccine is to lower the chances of being hospitalized due to influenza or pneumonia. It functions by prompting the immune system to generate antibodies that target and combat the influenza virus. This vaccine falls under the category of immunization agents, aimed at providing protection against four distinct strains of the influenza virus.

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, runny or stuffy nose, muscle or body aches, headaches, and fatigue. In some cases, it can lead to more severe complications, especially in older adults and those with weakened immune systems. The virus spreads through droplets when an infected person coughs, sneezes, or talks. It can also spread by touching surfaces contaminated with the virus and then touching the face.

  • 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 a variety of organisms, including bacteria, viruses, and fungi. Symptoms of pneumonia can include cough with phlegm or pus, fever, chills, and difficulty breathing. The disease can range from mild to severe, with severity often depending on the type of germ causing the infection, as well as the age and overall health of the individual. Pneumonia can be 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 weakened immune systems.

Trial detailsLast updated 2 Oct 2026
Age65+ yearsPhasePhase IIITrial ID2022-500657-17-00Protocol codeDANFLU-2Estimated enrolment339 700 patientsSponsorGentofte Hospital

sourced from the EU Clinical Trials Register and site verification

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On this site, “treatment” means an investigational medicine being studied in a clinical trial. Its safety and efficacy for the use being studied have not yet been confirmed, some participants may receive a placebo or a comparator medicine, and taking part does not guarantee any health benefit. The decision to take part is made by the doctor at the research site. This site is for information only and does not replace medical advice.

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