Dengue Vaccine FAQs for Doctors

Sunday, October 09, 2016 Stef dela Cruz, MD 0 Comments

Is the dengue vaccine safe? Is it effective? What happens if a patient receives only one dose instead of the recommended three? Can it be given to a two-year-old?

Because of its novelty, the dengue vaccine is the subject of many pressing questions, not to mention heated arguments. Even doctors who have been practicing for decades still have queries about the dengue vaccine, which is why coming up with a few informal FAQs have become a priority for me.

dengue vaccine FAQs

I know you must be so confused, what with the Department of Health having procured the vaccine for 1 million children in a three-billion-peso vaccine program despite still-ongoing trials (ethics in research and politics, anyone?), so let’s take a look behind the curtain and find out all that we can about the first-ever dengue vaccine: CYD-TDV (brand name Dengvaxia by Sanofi Pasteur).


Question #1: Is the dengue vaccine safe?

Because of the dichotomy of opinion on the subject of safety, the best people to ask this are those who have nothing to gain from the dengue vaccine – those who happen to be experts on epidemiology and evidence-based medicine.

I’ll bet my money on Drs. Tony and Inday Dans. Here’s what they have to say about the dengue vaccine’s safety in a short video.



Question #2: What are the side effects and risks?

Every medical intervention comes with side effects, which is why doctors should be experts at weighing risks versus benefits. However, when a new vaccine comes along, these aren’t always obvious at the get-go.

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In the video, one potentially deadly side effect was explained: antibody-dependent enhancement, which leads to severe dengue. Another lethal side effect is viscerotropism, which can have a mortality rate of almost 100 percent, explained Dans in a press conference.

Dr. Scott Halstead thus talked about the risks of the vaccine, saying, “It's clear as the nose on my face: Vaccine recipients less than 5 years old had five to seven times more rates of hospitalizations for severe dengue virus than placebo controls.”

Halstead has a lengthy list of credentials, including his being the founder of Children’s Vaccine Initiative and a past senior advisor of the Dengue Vaccine Initiative.

To prevent vaccine side effects, testing for antibodies (which can indicate previous exposure to dengue) is recommended. As explained in the video, those who are seronegative (no previous exposure) have a greater chance of getting severe dengue.


Question #3: Why is the dengue vaccine recommended for 9 years old and above?

“[The nine-year-old cutoff] was a post hoc analysis made after the results were seen,” explained Dr. Tony Dans.


Question #4: Should a patient who already received the first dose also be given the two other doses?

This is unclear. “Some think we should complete the program to maximize protection.”


Question #5: Did the World Health Organization really recommend that we use the dengue vaccine?

Short answer: No. However, they did recommend that any country interested in using the dengue vaccine should consider a list of factors.

The World Health Organization (WHO) Strategic Advisory Group of Experts on Immunization (SAGE) recommended that “decisions about introduction require careful assessment at the country level, including consideration of local priorities, national and subnational dengue epidemiology, predicted impact and cost-effectiveness with country-specific hospitalization rates and costs, affordability and budget impact.”

WHO SAGE said endemic countries (with a minimum of 70 percent dengue seroprevalence) may reap more benefits. Highly endemic countries, such as those with 90 percent seroprevalence, may vaccinate children 9 years old and above, while those with lower than 50 percent prevalence should start vaccination among kids 11 to 14 years old.


Question #6: Should the dengue vaccine be recommended in areas with a 70 percent (or 90 percent) seroprevalence in dengue, as per WHO advice?

The Danses find the 70-30 (and 90-10) seroprevalence cutoff problematic, saying it is inequitable and unfair to the poor.

“If 10 percent of the population is seronegative and you give them the vaccine, then you are putting 10 percent of the population at risk for potentially lethal side effects, such as severe dengue.”

Given how there’s a way to determine seroprevalence, it’s arguably reckless to recommend routine vaccination for everyone just because dengue is highly endemic. Is it not more ethical to recommend serotesting before vaccination, instead of recommending a potentially harmful vaccine for everyone, regardless of their antibody status?

Because serotesting cannot be afforded by the poor, they are the ones who will suffer.

“Testing for antibodies is not cheap. The underserved cannot afford it. While someone with money can get tested before getting the vaccine, a person who can’t afford it will be the one to risk getting lethal side effects.”

You may think that protecting 90 percent of the population is better than not protecting them at all, but remember that 10 percent of, say, 1 million people is still 100,000 people. That’s a lot of people you’re unnecessarily putting at risk for severe dengue, especially because there are safer, more effective, and cheaper means of preventing dengue (see Question #8).


Question #7: Is the dengue vaccine effective?

If by effective, you mean only 60 percent of people who get the expensive vaccine will be protected, then yes. But that’s a lukewarm answer – and we expect more if by giving the vaccine, we are possibly putting people’s lives in danger.

Dr Tony Dans“It is 60 percent effective in decreasing confirmed dengue cases in the short run. Actually, this is just modestly effective, considering how other vaccines are 90 to 95 percent effective. In the long run, it is not only ineffective; it is even possibly harmful.” 
-- Dr. Tony Dans

Statistics were based on the 2015 meta-analysis published in the New England Journal of Medicine.


Question #8: How can we prevent dengue if we can’t give the dengue vaccine?

There are many cheap, effective, and safe ways to prevent dengue. In fact, the Department of Health already launched an anti-dengue program that involved vector control and there’s no reason for this program to stop.

Additionally, targeting the vector (the mosquito) also helps protect the public from Chikungunya and Zika.

I would be happy to spend our dengue vaccine budget on a nationwide vector control program that can help keep mosquitoes – and three mosquito-borne diseases – away once and for all. Wouldn’t you?


Contribute to these dengue vaccine FAQs for doctors!

This is a work in progress. If you want to contribute answers, don’t be shy! If you have other questions you want to add to these FAQs, leave a comment or email me.

Stef dela CruzAbout the blogger
Stef dela Cruz is a vegan doctor and writer. She received the 2013 Award for Health Media from the Department of Health. She is the editor of The Manila Bulletin's Animal Scene Magazine. Get in touch if you want to invite her as a speaker!