To understand the current dengue outbreak, Associate Professor Alex Cook, Vice Dean (Research), revisits the situation in the years following Singapore’s independence and explains how the virus was limited in its transmission in the next few decades.
Fifty years ago, it was limited by number of people to infect, as most people had already been infected and were immune to the virus. As the country developed one of the world’s best vector control programmes, transmission was limited by availability of both people and mosquitoes to infect.
Over the years, it became very difficult for the virus to spread, the number of infections dropped and a new generation of Singaporeans — who were never infected and not immune to the virus — grew up and replaced the older, immune population. Thus, transmission today is limited by the availability of mosquitoes, not availability of susceptible people, which leaves us at a higher risk of an outbreak sparking off, like it has recently.
A/Prof Cook also shared that another reason why we see more dengue cases today is because we are getting better at diagnosing infections.
A recent study by the National Environment Agency, Ministry of Health and SSHSPH found that presently, the total number of infections may be as many as six times higher than what is reported. However, the same study found that the number of recorded cases in previous years is one in 14 infections, indicating that past outbreaks were much bigger than they looked.
“These contrasting trends imply that our doctors are getting better at diagnosing infections, through a better understanding of the signs of adult dengue and more testing of suspected cases. What this means is that although it looks like the dengue iceberg is getting bigger, actually all that has changed is that more lies above the surface, in plain sight,” said A/Prof Cook.
But because of Singapore’s early successes, dengue has become ever harder to control because of the population’s low immunity, he added.
He said, “Until a new vaccine becomes available that can be taken by those who have never been infected by dengue before, we need to maintain and enhance our vector control … mosquito breeding in our home is our problem, and we can do something about it by making a habit of doing the mozzie wipeout to protect ours and our neighbours’ families.”
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