By Dr Mar Faraco
The global expansion of dengue and the various outbreaks that occur each year in a wide range of tropical and subtropical destinations make this disease one of the most frequently addressed in travel medicine consultations.
Providing information about the importance of avoiding mosquito bites, as mosquitoes are the vectors that transmit the disease, is essential and takes priority in every consultation, given the various risks posed by diseases transmitted by these vectors. Vaccines or preventive medication are available for some of these diseases, but not for others. Traditionally, for many years, we have had the yellow fever vaccine, the possibility of malaria chemoprophylaxis and the Japanese encephalitis vaccine. In 2023, the dengue vaccine (Qdenga®) was authorised in Spain, and a few months ago a vaccine against chikungunya fever (Vimkunya®) was also authorised and marketed.
Recommending new vaccines is more complex for a simple reason: their novelty, which logically means that fewer data and less experience of use are available. Data from clinical trials and those generated through their progressive use in clinical practice help clinicians make a balanced decision based on the risks, benefits and costs associated with recommending these vaccines.
It is also important to have up-to-date information on dengue incidence at the destination and, wherever possible, to know which serotype or serotypes are circulating in each area, using resources such as the Dengue Visual Atlas.
The TAK-003 vaccine (Qdenga®) is a live attenuated vaccine administered as two doses separated by three months. It is approved for use in people over four years of age and has shown robust efficacy in clinical trials for the prevention of dengue:
- From 30 days to 12 months after the second vaccine dose, efficacy against dengue was 80.2%, and efficacy against hospitalised dengue was 95.4%.
- From 30 days to 18 months after the second dose, efficacy against dengue was 73.3%, and efficacy against hospitalisation due to dengue was 90.4%.
- At 4.5 years after the second dose, efficacy against virologically confirmed dengue was 61.2%, and efficacy against hospitalisation was 84.1%.
- At 7.5 years after vaccination, overall efficacy against dengue remained at 74.3%, and efficacy against hospitalised dengue at 90.6%.
These data include vaccinated individuals both with and without antibodies against dengue—that is, people who had or had not previously had dengue. It is important to bear in mind that Spanish travellers will normally have no pre-existing antibodies. This circumstance modifies and reduces vaccine efficacy: in people who are seronegative for previous dengue infection, vaccine protection will be strong against two of the four existing dengue virus serotypes, DENV-1 and DENV-2, but efficacy against DENV-3 has not been demonstrated, and data for DENV-4 remain too limited to assess protection.
Once the efficacy of the initial two-dose schedule, separated by three months, is understood, a very common issue arises in real-life consultations: travellers almost never attend three months in advance, and it is therefore often impossible to administer both doses before the trip, even though this is the schedule that reliably provides the benefits described above.
However, the same clinical trials provide additional data, including findings showing 82.1% vaccine efficacy from two weeks after the FIRST DOSE. To achieve the final efficacy figures and maintain protection over time, the schedule must always be completed with a second dose from three months after the first. Delaying the second dose for up to 12 months is accepted, but real-world data suggest that efficacy may decrease as the interval becomes longer. Therefore, when further travel is planned in the near future, it may be preferable to administer the second dose as close as possible to the three-month point.
In summary, the TAK-003 vaccine (Qdenga®):
- Provides early and significant protection from the first dose, reinforcing its potential usefulness as a vaccine for travellers in situations where immunity is needed before the two-dose schedule can be completed.
- The two-dose schedule must be completed, either in the destination country if the vaccine is available there or after returning from the trip, while respecting the minimum interval of three months. This is essential to maintain the overall demonstrated efficacy, as there are no long-term efficacy data for a single dose.
- There is no established maximum interval for administering the second dose; therefore, the schedule should be completed without restarting it.
Recommended reading
- https://vacunas.org/wp-content/uploads/2024/04/AEV_Dengue.pdf
- https://denguevisualatlas.com/es/destinos-con-dengue-que-serotipo-circula-aspecto-clave-en-la-decision-de-vacunacion-de-viajeros/
- https://www.sciencedirect.com/science/article/pii/S0264410X24009915
- https://denguevisualatlas.com/es/noticias/
