DENGUE fever is transmitted through mosquito bites and while mosquito control remains essential, vaccination offers an additional layer of protection. The World Health Organisation classifies dengue as one of the top 10 global health threats, with cases increasing tenfold from 500,000 in 2000 to more than five million in 2019.
The year 2023 saw an unprecedented surge in dengue cases, with the first-ever global figures exceeding 6.5 million and more than 6,800 deaths. Cases were reported in more than 80 countries across Africa, the Americas, South-East Asia, the western Pacific, and the eastern Mediterranean regions. Asia recorded the highest case fatality ratio in 2023. Bangladesh that year experienced its deadliest dengue outbreak in two decades, with 1,705 deaths out of 321,179 confirmed cases and a fatality rate of 0.53.
In addition, spatial and temporal shifts in dengue patterns were observed in 2022 which continued in 2023. Nepal and Bangladesh experienced spikes in the number of case earlier than usual. Cases in Nepal shifted from the Kathmandu Valley in 2022 to the southeast Terai region and hill districts in Gandaki province in 2023. India, in 2023, experienced an increase in cases in Kerala and northeastern states bordering Bangladesh compared with the previous year.
Vietnam has experienced dengue fever peaks almost every 10 years between 1980 and 2018. However, the period from 2019 to 2023 saw two epidemic peaks in 2019 and 2022. In 2022, Vietnam reported more than 367,000 dengue cases, second only to Brazil globally. The World Health Organisation estimates about 390 million dengue infections worldwide annually, with 96 million symptomatic cases, 500,000 hospital admission and 40,000 deaths.
Anyone can contract dengue fever, but children, pregnant women and people with chronic diseases or obesity are at higher risks. Untreated dengue can lead to severe complications, including hypotension, heart failure, kidney failure, hemorrhagic shock, multiple organ failure, cerebral hemorrhage and coma. Treatment now focuses on managing symptoms through blood filtration, plasma exchange and anti-shock measures. The cost of treating a severe case can cross the financial ability of most of the people.
The approved dengue vaccines are Dengvaxia and Qdenga, with varying efficacy and recommended populations. Dengvaxia has an efficacy of about 60鈥�80 per cent for preventing symptomatic dengue, but it is restricted to children aged 9鈥�16 year, with a confirmed prior dengue infection because of an increased risk of severe disease in seronegative individuals. On the other hand, Qdenga shows higher overall efficacy, with around 80 per cent protection against symptomatic dengue in both seropositive and seronegative individuals aged above four years.
Japanese company Takeda Pharmaceuticals invented Qdenga to protect people against all four dengue virus serotypes. Regulatory bodies that approved Qdenga include the European Medicines Agency and the European Commission in 2022, followed by other countries such as Indonesia, Great Britain, Brazil and Argentina. As of September, Qdenga was authorised in 40 countries and available in 27 countries, including Indonesia.
More important, Qdenga reduces the risk of hospital admission by up to 90 per cent. This is particularly crucial in countries such as Bangladesh, where a significant portion of the population has been infected with dengue at least once. Subsequent infections tend to be more severe, making timely vaccination a vital preventive measure. A vigorous consultation with all stakeholders and early engagement with Takeda to secure a substantial supply of the vaccine may reduce the annual burden of dengue fever.
People in Bangladesh frequent travellers to dengue-endemic areas and there is already a demand for the vaccine. The Vaccine Expert Group of the Swedish Society for Infectious Diseases Physicians have, therefore, reviewed the literature to guide and formulate recommendations on the use of Qdenga as a travel vaccine.
For travellers with previous known self-reported, hospitalised or policlinic testing for dengue fever, vaccination is recommended before travel to an endemic country. For dengue na茂ve-travellers, vaccination may be considered in individuals aged 4鈥�16 years irrespective of travel duration. For travellers aged 17鈥�60 years, vaccination is recommended considering only for long trips and related to travel destination. It has also been suggested a trip for more than six weeks to South-East Asia, a region with the highest global incidence of dengue fever. Since Qdenga has not yet been studied in individuals aged more than 60 years, vaccination is advised avoided in the group until data are available.
Travelling after only one dose should be avoided if possible, which is a challenge for most travelers coming at a short notice for travel medicine advice. It can be considered, especially in individuals with previous dengue fever, given that they receive the second dose after return. The recommendations are more cautious than in other non-endemic countries, especially regarding the upper age limit and should be continuously revised when more information and experience become available. For safe travel and living, the management of Aedes mosquitoes along with vaccination is essential.
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Professor Dr Md Golam Sharower is head of the entomology department at National Institute of Preventive and Social Medicine.
