Study on the Effects of the Dengue Vaccine Qdenga on Antibody Levels in Swedish Travelers

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What is this study about?

This clinical trial is focused on studying the effects of a vaccine called Qdenga, which is used to prevent dengue fever. Dengue fever is a disease caused by a virus transmitted through mosquito bites, and it can lead to symptoms like high fever, severe headache, and joint pain. The Qdenga vaccine is a live, attenuated vaccine, meaning it contains a weakened form of the virus that helps the body build immunity without causing the disease.

The purpose of this study is to understand how the Qdenga vaccine affects the levels of certain antibodies in the blood. Antibodies are proteins made by the immune system to help fight infections. Specifically, the study will look at whether the vaccine causes increased levels of antibodies that might react with other viruses similar to dengue, such as the viruses that cause tick-borne encephalitis (TBEV), yellow fever (YFV), Zika (ZIKV), and Japanese encephalitis (JE). This will be assessed by comparing antibody levels before and 90 days after receiving two doses of the vaccine.

Participants in the study will receive two doses of the Qdenga vaccine. The study will monitor the participants over a period to observe any changes in antibody levels. This research aims to provide valuable information on how the vaccine interacts with the immune system, particularly in people who may travel to areas where dengue fever is common. The study is expected to continue until 2027.

1 initial vaccination

Upon joining the study, you will receive the first dose of the Qdenga vaccine. This vaccine is a live, attenuated vaccine designed to protect against dengue fever. It is administered as a subcutaneous injection, which means it is injected under the skin.

The purpose of this vaccine is to help your body develop immunity against dengue fever, especially if you are planning to travel to areas where dengue is common.

2 second vaccination

You will receive a second dose of the Qdenga vaccine at a later date. This second dose is important to ensure that your body builds a strong immune response.

The second dose is also given as a subcutaneous injection. The timing of this dose will be communicated to you by the study team.

3 monitoring and follow-up

After receiving both doses of the vaccine, your antibody levels will be monitored. This involves taking blood samples to measure the levels of IgG antibodies in your blood. These antibodies help determine how well your body is responding to the vaccine.

The primary focus is to assess the levels of antibodies against other viruses like TBEV, YFV, ZIKV, and JE at day 90 after the second dose compared to before vaccination.

4 completion of study

The study is expected to conclude by November 1, 2027. By this time, all necessary data will have been collected, and your participation in the study will be complete.

You will be informed about the results and any findings related to your participation in the study.

Who Can Join the Study?

Able to participate in all parts of the study
Signed written informed consent
18 years of age or older
Negative pregnancy test (urine HCG) for women of childbearing potential. HCG is a hormone that is tested to confirm pregnancy.
Planning to travel to a country where dengue fever is common. The decision to get vaccinated will be made together with your doctor, following guidelines from the Swedish Society for Infectious Diseases Physicians.

Who Cannot Join the Study?

Participants must not have any serious health conditions that could interfere with the study.
Participants should not have received any other vaccines within a certain period before the study starts.
Participants must not have a history of severe allergic reactions to any component of the vaccine.
Participants should not be pregnant or planning to become pregnant during the study period.
Participants must not be breastfeeding during the study.
Participants should not have any immune system disorders, which means their body’s defense system is not working properly.
Participants must not be taking medications that affect the immune system, such as steroids.
Participants should not have participated in another clinical trial recently.
Participants must not have a history of drug or alcohol abuse.
Participants should not have any other condition that, in the opinion of the study doctor, makes them unsuitable for the study.

Where you can join this trial?

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Other Sites

Site Name	City	Country	Status
Region Vaesterbotten	Umea	Sweden

Trial status

Country	Status	Recruitment Start
Sweden	Recruiting	01.09.2025

Trial locations

Qdenga is a vaccine designed to protect against dengue fever, a disease caused by the dengue virus, which is transmitted by mosquitoes. The vaccine works by stimulating the body’s immune system to produce antibodies that can recognize and fight the dengue virus if the person is exposed to it in the future. In this clinical trial, the focus is on understanding how the Qdenga vaccine might affect the levels of certain antibodies that can also react to other similar viruses, such as those causing tick-borne encephalitis, yellow fever, Zika, and Japanese encephalitis. The trial aims to see if these antibody levels change significantly after receiving the Qdenga vaccine.

Investigated diseases:

Dengue fever

Dengue Fever – Dengue fever is a viral infection transmitted by mosquitoes, primarily the Aedes aegypti species. The disease begins with a sudden high fever, severe headaches, pain behind the eyes, and joint and muscle pain. As it progresses, a rash may appear, and mild bleeding symptoms such as nosebleeds or gum bleeding can occur. The fever typically lasts for 2 to 7 days, after which the patient may experience a drop in temperature and feel better for a short period. However, some individuals may develop more severe symptoms, including severe abdominal pain, persistent vomiting, and difficulty breathing. The disease is caused by one of four related viruses, and infection with one type does not provide immunity against the others.

Trial ID:

2025-520655-92-00

Protocol code:

The DenVacc Study

Trial Phase:

Therapeutic confirmatory (Phase III)

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Study on the Effects of the Dengue Vaccine Qdenga on Antibody Levels in Swedish Travelers

What is this study about?

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