May 13, 2024
SINGAPORE – Even as dengue numbers soar worldwide, experts say it remains to be seen how the record figures elsewhere will impact the number of infections in Singapore.
To date, there have been more than five million dengue cases and more than 2,000 dengue-related deaths globally since the beginning of 2024, according to the European Centre for Disease Prevention and Control.
Parts of Central and South America are reporting record numbers of the disease, with Brazil seeing more than one million dengue cases in the first two months of 2024.
In comparison, there were about six million dengue cases worldwide for the whole of 2023, with more than 6,000 dengue-related deaths reported that year.
Still, the high numbers seen in other countries may not impact Singapore, say experts.
Dengue expert Tikki Pang, a visiting professor at NUS’ Yong Loo Lin School of Medicine, said that while numbers could potentially spike, this is unlikely due to the relatively low passenger traffic between Latin America and Singapore.
International Society for Infectious Diseases president Paul Tambyah said: “Usually we are concerned about travellers bringing in new serotypes or variants, but it seems like there is already a lot of diversity in the dengue strains circulating, so I think that the impact of incoming or returning travellers is likely to be low.”
There are several possible reasons for the worldwide spike in dengue cases.
Professor Tambyah noted that the World Health Organisation has pointed to the impact of El Nino – a climate pattern associated with the unusual warming of surface waters in the eastern tropical Pacific Ocean – on the life cycle of the Aedes mosquito.
“When the temperature rises 1 or 2 deg C, the mosquito can live a bit longer and bite more people, thus spreading the virus more widely and effectively,” he said.
Professor Duane Gubler – who chairs the National Environment Agency’s dengue expert advisory panel and is emeritus professor at Duke-NUS Medical School – pointed to other trends, such as urban growth in tropical cities, with inadequate sewage and waste management providing a habitat for mosquitoes to breed, as well as inadequate public health infrastructure, as the drivers of disease.
He added that while weather is an important influence on dengue numbers, it is unclear how much of a role climate change plays.
“Most of the modelling studies that predict large increases in numbers of cases are flawed because they look mainly at temperature changes and ignore the complexity of other factors that influence transmission. Plausibility is not proof of causality,” he said.
Singapore, meanwhile, has seen more than 5,000 dengue cases in the first quarter of 2024 – more than double that of the same period in 2023 – with seven deaths from the disease.
While Singapore has strong, well-implemented measures against dengue, Prof Pang said more intensive efforts could be necessary to further control the spread of dengue here.
He suggested that mosquito-breeding regulations could be enhanced and dengue hot spots could be more closely monitored.
Prof Tambyah said that while vaccination has been touted as a solution to the disease, dengue vaccine development has been “very tricky” over the years.
He said that Dengvaxia – currently the only dengue vaccine available here, and only to those between 12 and 45 years old who have previously been infected – has limited utility due to the increased risk of developing severe dengue in those who have never been infected.
He added that while another vaccine, Qdenga – which is currently approved in countries such as Brazil and Indonesia – does not have that problem, its efficacy stands at 61 per cent, which he described as being “a bit lower” than needed to eradicate dengue.
Japanese pharmaceutical firm Takeda previously submitted Qdenga for approval here in 2022, but the Health Sciences Authority in 2023 said the company had withdrawn its application.
Another vaccine in development, produced by Brazil’s Butantan Institute, promises to protect 80 per cent of those who receive the vaccine against all four dengue serotypes.
“Used alone, neither vaccination nor mosquito control will be entirely effective, but combined use in an integrated programme should be very effective in preventing epidemic dengue,” said Prof Gubler. “Hopefully, Singapore will license all available dengue vaccines in the near future and use them for this purpose,” he added.