Live Attenuated Influenza Vaccine (LAIV) and Immune Response in the Nasopharynx of Young Children with Influenza

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What is this study about?

This study focuses on understanding how the immune system responds to Live Attenuated Influenza Vaccine (LAIV) in young children. Influenza is a common respiratory illness caused by influenza viruses that can lead to fever, cough, sore throat, body aches, and fatigue. The LAIV is a nasal spray vaccine that contains weakened influenza viruses that do not cause illness but stimulate the immune system to develop protection against influenza.

The purpose of this research is to examine how the immune system in the nose (nasal mucosa) responds after children receive the nasal spray influenza vaccine. The study will involve children receiving two doses of the nasal spray vaccine and collecting samples from the nasal lining to measure the presence of vaccine viruses and immune responses. Small absorptive devices will be used to collect fluid from inside the nose at various timepoints after vaccination.

Researchers will analyze these samples to understand how the immune system in the nose reacts to the vaccine, including the production of protective antibodies (proteins that help fight infection). They will also monitor for any respiratory symptoms through questionnaires completed by parents. Blood samples may be collected from some participants, though this is optional.

1 First visit and initial assessment

You will receive your first dose of Fluenz nasal spray (also called LAIV, which stands for Live Attenuated Influenza Vaccine). This is a spray that goes into your nose and contains weakened flu viruses that help your body build protection against the flu.

The healthcare team will collect a sample of fluid from the lining of your nose using a small device called a nasosorption. This is a gentle procedure that absorbs a tiny amount of fluid from inside your nose.

If you and your parents have agreed to the optional blood test, a small blood sample will be taken to measure your immune system’s response.

2 Home monitoring after first dose

You will need to store some samples in your home freezer during the study period.

Your parents will help you complete daily questionnaires about any symptoms you might experience, such as runny nose, cough, or sneezing.

Regular nasosorption samples will be collected to check if the vaccine viruses are present in your nose (called ‘viral shedding’) and how your body’s immune system is responding to the vaccine.

3 Second dose visit (28 days after first dose)

Approximately 28 days (about 4 weeks) after your first dose, you will return to receive a second dose of the Fluenz nasal spray.

Another nasosorption sample will be taken from your nose before receiving the second dose.

If you are participating in the optional part of the study, another small blood sample will be taken to compare with your first sample.

4 Home monitoring after second dose

Similar to after the first dose, you will continue to store samples in your home freezer.

Your parents will help you complete the daily symptom questionnaires.

More nasosorption samples will be collected to monitor viral shedding and immune responses after the second dose.

5 Final assessment

The study team will collect all the samples you’ve stored in your home freezer.

A final nasosorption sample will be taken to check how your immune system has responded to both doses of the vaccine.

This will complete your participation in the study, which is expected to run until March 31, 2026.

Who Can Join the Study?

Age between two and seven years old
Parents must be able and willing to follow all study procedures
Parents must have a freezer at home to store samples
Willingness to receive an intranasal LAIV (a flu vaccine given as a nasal spray instead of an injection)
Understanding that the study involves receiving two doses of the nasal spray vaccine
Understanding that shedding (when virus particles from the vaccine are released from the nose) will be measured after vaccination
Blood donation is optional (not required) for the study

Who Cannot Join the Study?

Children who have already received the nasal spray flu vaccine (LAIV) in the current season
Those with a weakened immune system (when the body’s defenses against illness are not working properly)
Children who have severe asthma (a condition causing breathing difficulties) or active wheezing
Those allergic to any components of the vaccine
Children taking medications called salicylates (like aspirin)
Those who are pregnant
Children with a history of Guillain-Barré syndrome (a rare condition affecting the nervous system)
Those with active respiratory illness or fever
Children who have close contact with someone who has a severely weakened immune system
Those who have received another vaccine within the past 4 weeks
Children who have a history of severe allergic reaction to eggs or previous flu vaccines

Where you can join this trial?

Verified and Recommended Sites

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Verified Sites

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Other Sites

Site Name	City	Country	Status
Leiden University Medical Center	Leiden	The Netherlands

Trial status

Country	Status	Recruitment Start
The Netherlands	Not recruiting	02.06.2025

Trial locations

Investigated drugs:

INFLUENZA VIRUS B/AUSTRIA/1359417/2021 – LIKE STRAIN (B/AUSTRIA/1359417/2021, MEDI 355292)

LAIV (Live Attenuated Influenza Vaccine) is a type of flu vaccine that contains weakened flu viruses. It is given as a nasal spray (sprayed into the nose) rather than as an injection. In this study, LAIV is being used to understand immune responses in the nose and throat area. The researchers are looking at how the body’s immune system reacts to the vaccine to better understand how it provides protection against the flu.

Influenza is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It is characterized by sudden onset of fever, muscle aches, headache, malaise, cough, sore throat, and nasal congestion. Influenza is known for its ability to spread rapidly through populations, especially during seasonal epidemics. The disease typically resolves within one to two weeks in most healthy individuals, though fatigue may persist longer. Influenza viruses continuously evolve through genetic changes, which is why the disease can recur and why annual vaccination is recommended. The severity of symptoms can vary widely among individuals, with some experiencing mild illness while others develop more severe manifestations.

Trial ID:

2024-513933-18-00

Trial Phase:

Therapeutic confirmatory (Phase III)

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Live Attenuated Influenza Vaccine (LAIV) and Immune Response in the Nasopharynx of Young Children with Influenza

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?