A dengue vaccine used before travel appears to be generally well tolerated in people from regions where dengue is not regularly found, according to new real-world data from Catalonia.

The study, involving 1,028 people who received the TAK-003 vaccine, reported no serious adverse events after vaccination. Most reactions were mild or moderate and short-lived, including injection-site pain, headache, tiredness and general malaise.

The findings matter because dengue is becoming a more frequent concern for international travellers. They do not, however, remove the need for individual travel health advice or careful mosquito-bite prevention.

Why dengue matters for travellers

Dengue is a viral infection spread by Aedes mosquitoes, particularly Aedes aegypti and Aedes albopictus. These mosquitoes often bite during the day and can live close to people in towns and cities.

The infection is common in many tropical and subtropical regions, including parts of Asia, Latin America, Africa and the Pacific. Dengue transmission has been documented in more than 100 countries, and more than half of the world’s population is estimated to live in areas, including Malaysia, where infection is a risk.

Many dengue infections cause no symptoms or a flu-like illness. When symptoms occur, they may include high fever, severe headache, pain behind the eyes, muscle and joint pain, rash, nausea and fatigue.

A small proportion of cases become severe. Severe dengue can involve bleeding, organ problems, shock and, rarely, death. Risk can be influenced by factors such as previous infection with a different dengue virus type.

Dengue has also become one of the leading causes of fever in people travelling to areas where the virus is endemic, meaning it circulates regularly in the local population. Climate change, the spread of mosquito vectors and international travel are all contributing to wider concern about dengue.

What the Catalonia study examined

The new evidence comes from a human pharmacovigilance study, a type of safety monitoring that tracks possible adverse events after a medicine or vaccine is used in routine care.

The study was led by the Barcelona Institute for Global Health, together with Hospital Clínic Barcelona, and was published in The Lancet Regional Health Europe.

Researchers followed travellers who received TAK-003 at eight travel health centres in Catalonia between January and December 2024. Most participants were adults preparing to visit areas where dengue is present.

In total, the study included 1,028 people and assessed 1,851 vaccine doses.

TAK-003, marketed in some countries as Qdenga, is a live attenuated tetravalent dengue vaccine. “Live attenuated” means it uses weakened forms of the virus. “Tetravalent” means it is designed to target all four dengue virus serotypes, or types.

The researchers recorded adverse events after each dose. They also examined whether factors such as age, sex, previous dengue infection, existing medical conditions or receiving other vaccines at the same visit were linked with a higher chance of side effects.

What the study found

No serious adverse events were reported after the 1,851 TAK-003 doses included in the study.

More than half of participants reported at least one adverse event, but these were mostly mild or moderate and short-lived. Reactions were less frequent after the second dose than after the first.

The most commonly reported symptoms were pain at the injection site, headache, fatigue and general malaise.

In plain language, the findings suggest that TAK-003 had a favourable short-term safety and tolerability profile in this group of travellers from a non-endemic region.

Some groups reported more reactions

The researchers found that adverse events were more likely in some groups.

Female participants had a higher likelihood of reactions, mainly local reactions such as pain or discomfort where the injection was given.

People with a previous dengue infection were also more likely to report adverse events. In this group, reactions were more often systemic, meaning symptoms affecting the body more generally, such as fever or malaise.

Participants who received another flavivirus vaccine at the same time also had a higher risk of adverse events. Flaviviruses are a family of related viruses that includes dengue, yellow fever, Japanese encephalitis, Zika and West Nile virus. Yellow fever vaccine was one example mentioned by the researchers.

The study did not find increased reactogenicity in people aged over 60 or in those with comorbidities. Reactogenicity refers to expected short-term reactions after vaccination, such as fever, soreness or tiredness. Because subgroup numbers can affect how much confidence researchers have in these comparisons, this finding should still be interpreted cautiously.

The researchers also found no increased likelihood of adverse events when TAK-003 was given at the same time as non-flaviviral vaccines. This may be useful in travel clinics, where several vaccines are often given before a trip.

How the vaccine works

Dengue is caused by four closely related virus serotypes: DENV-1, DENV-2, DENV-3, and DENV-4. Infection with one serotype does not reliably protect against the others.

TAK-003 is designed to target all four serotypes, although vaccine performance may vary by serotype and by whether a person has had dengue before.

After vaccination, immune cells recognise the weakened vaccine viruses. This prompts the body to produce immune responses, including antibodies and other immune cell activity.

If the vaccinated person later encounters dengue, the immune system may be better prepared to recognise the virus and respond more quickly.

Short-term side effects can occur because vaccination activates the immune system. Pain at the injection site is usually linked to local immune activity where the vaccine was given. Symptoms such as headache, tiredness or fever can occur when immune signalling affects the wider body.

These reactions are not the same as having dengue infection. They are usually temporary signs that the immune system has responded to the vaccine.

How strong is the evidence?

This study adds useful real-world safety data, especially because evidence in travellers from non-endemic regions has been limited.

Its strengths include the number of participants, monitoring after vaccination and the fact that it reflects routine travel health practice rather than only a tightly controlled trial setting.

However, the findings have limits.

The study was observational, so it can show patterns and associations but cannot prove that every symptom reported after vaccination was caused by the vaccine. Some symptoms may have occurred by chance, especially when people were also preparing for travel or receiving other vaccines.

The study was not large enough to rule out very rare serious adverse events. Detecting rare risks requires much larger populations and longer monitoring.

The findings mainly concern short-term tolerability. They do not answer all questions about long-term safety, how long protection lasts or how well the vaccine prevents dengue illness in different traveller groups.

The study was also conducted in Catalonia, so its results may not apply equally to all populations or healthcare settings.

What this means for travellers

For people considering travel to areas where dengue is common, the findings are reassuring but do not change the basic approach to travel health planning.

Travellers should seek advice from a qualified travel health professional before visiting areas with dengue risk. Whether TAK-003 is suitable depends on factors such as destination, trip length, age, medical history, immune status, pregnancy status, previous dengue infection and timing before departure.

Because TAK-003 is a live vaccine, it is not suitable for everyone, including some people with immune suppression and those who are pregnant, in line with product guidance and local clinical advice.

Vaccination also does not replace mosquito-bite prevention.

People travelling to dengue-risk areas are still advised to reduce bites by using effective insect repellent, wearing clothing that covers the skin where practical, staying in accommodation with screens or air conditioning, and removing standing water where mosquitoes breed.

How this fits with current prevention

Dengue prevention has long relied mainly on mosquito control and personal bite protection. These measures remain essential because no vaccine offers complete protection and mosquitoes can transmit other infections as well.

Vaccination may add another layer of protection for some travellers. The Catalonia study supports the short-term safety of TAK-003 in a real-world European travel clinic setting, including in older adults and people with existing medical conditions in the study sample.

At the same time, vaccine decisions need to balance potential benefit and risk. A person travelling briefly to a lower-risk area may have a different risk profile from someone spending several months in a high-transmission setting.

Public health authorities and travel medicine specialists will need continued evidence on safety, effectiveness and best use in different groups.

What remains unknown

Several questions remain unanswered.

Researchers still need more data on rare adverse events, especially in larger and more varied populations. Longer follow-up is also needed to assess long term safety over time.

More evidence is needed on vaccine effectiveness in travellers from non-endemic regions, including people with and without previous dengue infection.

Further research should also clarify how best to use TAK-003 alongside other vaccines, particularly other flavivirus vaccines, and whether certain groups need more tailored counselling about expected reactions.

The finding that previous dengue infection was linked with more systemic reactions is worth further study, but it should not be overinterpreted without more data.

The wider picture

This real-world study suggests that TAK-003 was generally well tolerated among travellers in Catalonia, with no serious adverse events reported after 1,851 doses.

Most reactions were mild or moderate and were reported less often after the second dose. The results add useful evidence for travel medicine, particularly for adults from regions where dengue is not endemic.

For now, the takeaway is cautious reassurance. Dengue remains a growing travel health concern, and vaccination may help protect some people, but decisions should still be made through individual medical advice and alongside careful mosquito-bite prevention.