Dengue Vaccine Hesitancy Undermines Efforts To Curb Rising Cases

The  ‘Anemia Screening and Dengue Vaccination Drive for Children’ community health event on June 20, organised by Universiti Malaya’s Faculty of Medicine, saw a good turnout, with people filling in forms, checking how much or how little muscle they have compared to body fat, undergoing blood screening and finally, in a side room, getting the vaccine against dengue.

“Many people have come,” observed Prof Dr Rafdzah Ahmad Zaki, professor of epidemiology and public health at Universiti Malaya (UM). She sounded satisfied and slightly relieved.

Two weeks ago, UM organised a similar screening and vaccination drive in Ampang, Selangor. They had expected 300 people to show up, but fewer than 100 came.

The reason, Dr Rafdzah suspects, is that people in the community thought the event was a vaccination drive and not a health screening.

UM’s Anemia Screening and Dengue Vaccination Drive for Children programme started in May and runs till August. Throughout the week, when there is no community event, they offer the same services at Universiti Malaya Medical Centre (UMMC).

“A few said that when they heard about the dengue vaccine, they were afraid (to come),” Dr Rafdzah told Bernama. She added that several people with appointments for their children to undergo screening at UMMC had called to cancel, citing the dengue vaccination as the reason.

What she and her colleagues have been hearing worries them, especially in the face of what’s coming. Malaysia is at the brink of a triple threat related to climate change: an incoming extreme El Niño event – dubbed Godzilla El Niño, heralding extremely hot and dry conditions with bouts of heavy rain – from June till early next year, as well as soaring dengue cases year to year and high anemia rates among children in Malaysia. 

 

Dengue, an infectious disease also known as break-bone fever, is caused by a virus transmitted by the Aedes aegypti mosquito and is endemic in Malaysia and other countries along the equator. Usually associated with hot and humid climes, dengue is no longer considered just a tropical disease. Due to global warming, dengue has been found in temperate zones as well, including Italy, France, Spain and North America.

To make matters worse, excessive heat also aids the mosquitoes’ life cycle.

“When it's hot, the incubation period for the mosquito is shorter. So the eggs hatch earlier, so you get more mosquitoes, right?” Professor Tan Sri Dr Jemilah Mahmood, executive director of Sunway Centre for Planetary Health, told Bernama via Google Meet.

“(The incubation) kind of speeds up so that they breed in more places and for more months of the year rather than specific times (making the mosquitoes present year round).”

The effects of the hot weather and dengue are already present in Malaysia. The heatwave began in March this year. Health Minister Datuk Seri Dr Dzulkefly Ahmad said this year, as of June 13, there were 33,367 dengue cases nationwide, an increase of 20.7 percent compared with the same period last year. Eleven days later, Malaysia recorded 4,220 more cases, according to data on the government’s i-Dengue portal.

Hoping that the hot weather will dry out standing water does not work. Dr Rafdzah warned that the dengue virus also infects mosquito eggs, which can survive without water up to six months.

Studies have found that El Niño increases the incidence of dengue. One such study, ‘Rising dengue risk with increasing El Niño–Southern Oscillation amplitude and teleconnections,’ by Tian, Y, et al and published in leading science journal  ‘Nature’ in September 2025, found that 63 percent of dengue cases in the Americas and Asia were attributable to El Niño events in 1982 to 1983, 1997 to 1998, 2015 to 2016, and 2023 to 2024 [https://pmc.ncbi.nlm.nih.gov/articles/PMC12480917].

“Due to human-induced warming, El Niño events and teleconnections may cause a 39.0–81.7 percent increase in cumulative (dengue) cases in 2020–2099,” the researchers concluded.

Couple that with high anemia rates in Malaysia due to iron deficiency among children. According to Dr Jemilah, excessive temperatures can worsen anemia, which in turn increases health risks such as strokes.

Anemia is estimated to affect 46.5 percent of Malaysian children under five, according to the Ministry of Health’s 2022 ‘National Health and Morbidity Survey (NHMS): Maternal and Child Health’. Anemia is characterised by low red blood cell count and causes fatigue, as well as poor cognitive abilities and motor skills.

At the Kepong community health event, Dr Rafdzah said they wanted to screen children aged seven to 12 years for anemia because there is not enough anemia data on children in that age group.

“Not many people know that those who suffer from anemia, if they get infected with dengue, their symptoms will be much (more) severe,” she added.

Dengue causes the bone marrow to decrease platelet production and damages blood vessel walls, which can lead to internal bleeding and organ failure. For anemic people, who have fewer red blood cells to begin with, any blood loss is dangerous. Their bone marrow is also weaker due to iron deficiency.

A second dengue infection is usually more severe than the first.

Besides ensuring there is no standing water for mosquitoes to breed, health officials are also encouraging everyone to take the two-dose Qdenga vaccine, the only vaccine approved for dengue in Malaysia.

But not many are taking up the dengue vaccine. At UM’s community health event in Kepong, out of 42 children who came for screening, 33 agreed to get the vaccine. 

 

In an op-ed on ASEAN Dengue Day in ‘The Edge Malaysia’ on June 15, head of Dengue Prevention Advocacy Malaysia Dr Zulkifli Ismail called for the Qdenga dengue vaccine to be included in the National Immunisation Programme (NIP), saying that relying solely on Wolbachia-infected mosquitoes or behaviour-change campaigns to fight dengue was no longer enough.

“We cannot afford to treat this vaccine as a niche product for the informed few and the rich. The Health Ministry must immediately launch a holistic mass public awareness campaign and negotiate with the (vaccine) manufacturer,” he wrote.

With vaccine hesitancy on the rise, leaving a crucial vaccine as optional seems unwise.

Vaccine hesitancy, colloquially known as anti-vaxx, is a spectrum ranging from those who are completely against vaccines to those who are willing to be vaccinated against certain diseases or after certain criteria are met, such as ascertaining the halal status of the ingredients in the vaccine. Research has found that vaccine hesitancy has increased in Malaysia in the past two decades, with the number of vaccine-preventable infectious diseases such as measles and pertussis on the rise.

The 2022 NHMS found that vaccine hesitancy rates increased 10 times from 2016 to 2022, from 0.1 percent to one percent. Penang recorded the highest rate of unvaccinated or incomplete vaccination at 40.4 percent, followed by Kelantan at 28.9 percent and Kuala Lumpur and Putrajaya at 27.2 percent. The survey also found that five percent of parents have vaccine hesitancy. 

There is no data on dengue vaccinations as it is not included in the NIP.

In 2016, the Philippines mass immunised schoolchildren with Dengvaxia, a dengue vaccine. What was not known at the time was that only those who had dengue before should get the vaccine. If someone had never had dengue before, Dengvaxia increased the chance of a severe case.

On allegations that the vaccine caused the deaths of 14 vaccinated schoolchildren, a Philippine Department of Health and University of the Philippines-Philippine General Hospital task force found no evidence linking the vaccine to the schoolchildren’s deaths. Of the 14 deaths, nine were caused by other illnesses such as congenital heart disease; and two resulted from vaccine failure (meaning the vaccine did not protect them from dengue). As for the rest, the cause remained unexplained. During the same period, unvaccinated children had also died from dengue.

Dr Rafdzah said recent news reports of the withdrawal of a one-dose dengue vaccine undergoing human trials in Brazil while health authorities investigated two deaths associated with it did not help encourage people to take the dengue vaccine despite its benefits.

“People are scared of vaccines. In fact, any vaccine,” she said, adding that misinformation on social media and unnuanced reporting in news reports are contributing further to the trust deficit.

 

For some who are supportive of vaccines, it is not the misinformation that is the hurdle but a lack of it.

At the recent community health event in Kepong, Tan Pei Syien, a 38-year-old mother of two boys, waited patiently for her elder son to finish giving a blood sample. She told Bernama she brought her sons to get the dengue vaccine.

“Before this, I never knew about the dengue vaccine,” she said, adding that she is interested in getting the vaccine herself. 

Other adults at the event were not as supportive. 

Kelvin Yee, who is head of Public Information at the Petaling Garden Kuala Lumpur Residents’ Welfare Association, said it was difficult to convince the older generations to attend the health screening or get the dengue vaccine, which is also available for adults at UMMC at RM150 per dose.

Even the death of a 25-year-old man from dengue last July in Petaling Garden Kuala Lumpur, which is located in Kepong and is a dengue hot spot, could not convince the elderly residents, a majority of whom are senior citizens.

Instead, Yee said the residents are more into keeping their surroundings clean and ensuring there are no mosquito breeding grounds.  

“A resident died because of dengue. So they (other residents) are afraid. There’s awareness after (the) death," he said.

He added that when checking for the source of the infection, public health authorities found that the tank above the late resident’s house was full of mosquito larvae.

Dr Rafdzah agreed that community cleanliness is crucial in battling dengue, but hoped that it does not take a death in the neighbourhood before the community would work together to prevent the disease.

“If you are trying to protect your home but your neighbour doesn’t want to protect (theirs), then it’s no use,” she said.

And for added protection, especially for children, people with anemia, the elderly and high-risk populations, health experts recommend getting the vaccine.

“If you're at very high risk, then you know it may be a case to consider (taking the vaccine),” added Dr Jemilah.