No 7/9 - 2025

Revised recommendation regarding vaccination against dengue fever among travelers

A vaccine providing protection against dengue fever, Qdenga^®, has had approval by EMA since 2023, EPI-NEWS 14/2023.

Qdenga^® is a live attenuated vaccine that contains weakened variants of the dengue virus serotypes 1 to 4 (DENV1, DENV2, DENV3, DENV4).

The vaccine is administered as a subcutaneous injection. The approved vaccination regimen consists of two vaccine doses given at least 3 months apart. In connection with travel, dose number two must be given at least one week before departure.

Qdenga^® has been approved by EMA for vaccination of adults, adolescents, and children from 4 years of age. However, WHO recommends that, until further data on the vaccine’s effectiveness and safety are available, the use of Qdenga^® for travelers be limited to persons aged 6 to 60 years.

The vaccine must not be given to pregnant or breastfeeding individuals or to persons with congenital or acquired immune suppression.

The evidence for the protective effect and side effects of the Qdenga^® vaccine mainly comes from clinical studies among children and adolescents (4-16 years) living in countries with endemic dengue occurrence. There is still only limited data on the vaccine’s effect among adults and among travelers from non-endemic countries.

Among vaccinated children who have previously been infected with dengue (sero-positive), protection against all four dengue serotypes has been demonstrated. Among previously uninfected individuals (sero-negative), however, protection has only been shown against serotypes DENV1 and DENV2, with no protection against DENV3 and DENV4.

In connection with Qdenga^® vaccination, a high occurrence of vaccine-induced viremia has been seen in previously uninfected individuals, accompanied by mild-to-moderate clinical symptoms in the form of headache, joint pain, muscle pain, and rash, which typically appear about a week after the first vaccine dose (49%) but less frequently after the second dose (16%), according to the product summary.

As further stated in the product summary, it is not yet known whether the vaccine’s lack of protection against serotypes DENV3 and DENV4 may lead to increased severity of dengue fever if a previously uninfected person contracts one of these types after Qdenga^® vaccination. This issue was observed with the first approved dengue vaccine, Dengvaxia^®. Therefore, WHO recommends that previously uninfected travelers considering vaccination with Qdenga^® be informed about this potential risk.

Revised recommendation regarding the use of the Qdenga^® vaccine against dengue fever

Based on the above, SSI recommends, until further data on Qdenga^®’s effectiveness and safety in previously uninfected individuals are available, that Qdenga^®, as a general rule, only be used for travelers who have previously been infected with dengue. This corresponds to the latest national recommendations in several other European countries.

Qdenga^® may still be considered for travel and long-term stays in areas with a known high prevalence of dengue, typically 4 weeks or more, or for example in cases of expatriation, but as a general rule, only for individuals who have previously had dengue fever.

Travelers who have not previously been infected with dengue but still consider vaccination with Qdenga^® should be thoroughly informed about: 1) the vaccine’s lack of protection against serotypes DENV3 and DENV4, 2) the potential risk of severe illness when infected with DENV3 and DENV4 during the trip, and 3) the frequent occurrence of viremia and mild-to-moderate clinical symptoms (headache, joint pain, muscle pain, rash) after the first dose of Qdenga^®.

It is also important to emphasize to travelers that vaccination with Qdenga^® is only a supplement to the primary protection against dengue, which consists of avoiding mosquito bites, i.e., through careful use of mosquito repellent and balm, mosquito nets, and skin-covering clothing, which also protects against infection with a range of other mosquito-borne diseases.

Finally, travelers should be aware that dengue infection in most travelers causes no or only mild illness, and that severe dengue fever is rarely seen among travelers. However, individuals who are infected for a second time are at a higher risk of becoming more seriously ill. Further information on dengue fever can be found in SSI’s Disease Lexicon.

(L.S. Vestergaard, A.V. Søndergaard, P. Valentiner-Branth, P.H. Andersen, Department of Infectious Disease Epidemiology and Prevention)