Qdenga vaccine: to have or not to have

[JackGats]

It seems now the Qdenga vaccine gets recommended by many countries even for seronegatives. Many countries still recommend against it for seronegatives though:

 

https://academic.oup.com/jtm/article/32/3/taaf023/8064715

 

According to ChatGPT the vaccine affords low protection (something like 40%) against infection, but high protection (80%) against hospitalisation. This is reminiscent of the Covid vaccines (please no rant about the Covid vaccines!)

 

I'm still sitting on the fence.

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4 minutes ago, JackGats said:

It seems now the Qdenga vaccine gets recommended by many countries even for seronegatives. Many countries still recommend against it for seronegatives though:

 

https://academic.oup.com/jtm/article/32/3/taaf023/8064715

 

According to ChatGPT the vaccine affords low protection (something like 40%) against infection, but high protection (80%) against hospitalisation. This is reminiscent of the Covid vaccines (please no rant about the Covid vaccines!)

 

I'm still sitting on the fence.

Here's what AI says:

Key Features of Qdenga:

• Protection: Qdenga protects against all four dengue virus serotypes (1, 2, 3, and 4).

• Dosage: The vaccine is administered in two doses, with the second dose given three months after the first.
•  

• Efficacy: Qdenga has shown high efficacy in preventing dengue fever (80.2%) and hospitalization (90.4%).

• Safety: The vaccine is generally well-tolerated, with no serious adverse events linked to it.
   

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Anyway, thanks for letting me know it exists.

[GroveHillWanderer]

3 hours ago, JackGats said:

It seems now the Qdenga vaccine gets recommended by many countries even for seronegatives. Many countries still recommend against it for seronegatives though:

 

https://academic.oup.com/jtm/article/32/3/taaf023/8064715

 

According to ChatGPT the vaccine affords low protection (something like 40%) against infection, but high protection (80%) against hospitalisation. This is reminiscent of the Covid vaccines (please no rant about the Covid vaccines!)

 

I'm still sitting on the fence.

 

The WHO position paper that your linked article references in regard to Qdenga for seronegative individuals, states the following: 

 

Quote

Until the efficacy–risk profile for DENV3 and DENV4 in seronegative persons has been more thoroughly assessed, WHO does not recommend the programmatic use of TAK-003 [Qdenga] vaccine in low to moderate dengue transmission settings.

 

So unless you're at high risk of Dengue infection, maybe Qdenga is not really indicated at this time (until more data is available).

 

However the efficacy figures the WHO paper gives are much higher.

 

Quote

During the 51 months of follow-up, seropositivity rates in baseline seronegative subjects consistently

remained >98% against DENV2, and >80% against the other 3 serotypes.

 

https://www.who.int/publications/i/item/who-wer-9918-203-224?form=MG0AV3

[short-Timer]

I got it. So glad I did. 

[GroveHillWanderer]

On the other hand, the paper also states that the data on risks for seronegative individuals for DENV3 and 4 is limited, precisely because infections with those serotypes is less common. That seems to be true for Thailand also. 

 

"In Thailand, DENV-2 and DENV-1 are the most common dengue serotypes, although DENV-3 and DENV-4 also circulate. Studies in Southern Thailand and other regions have shown DENV-2 as a dominant serotype in some years, followed by DENV-1, DENV-3, and DENV-4."

 

Epidemiology and costs of Dengue in Thailand

 

https://pmc.ncbi.nlm.nih.gov/articles/PMC9810168/

 

So it seems as though the risk of getting DENV3 or 4 is lower that for the other two serotypes.

[Captain Flack]

I have moved the topic to health and wellness, where it is better suited.

[LosLobo]

Seems there may be some limitations on age group over 60 in Thailand based on limited clinical data for that particular group.

'Can be administered to anybody 4 – 60 years old'

https://www.bangkokhospital.com/en/content/dengue-vaccine

[GroveHillWanderer]

6 minutes ago, LosLobo said:

Seems there may be some limitations on age group over 60 in Thailand based on limited clinical data for that particular group.

'Can be administered to anybody 4 – 60 years old'

https://www.bangkokhospital.com/en/content/dengue-vaccine

True, but there's no a priori reason for supposing that the vaccine will not work, or will have any significantly different safety profile in people over 60, as far as I'm aware.

[LosLobo]

9 minutes ago, GroveHillWanderer said:

True, but there's no a priori reason for supposing that the vaccine will not work, or will have any significantly different safety profile in people over 60, as far as I'm aware.

I agree — and in the West, you can usually discuss it with your healthcare provider, and based on their assessment, they would likely approve it if appropriate.

[NanLaew]

4 hours ago, short-Timer said:

I got it. So glad I did. 

 

Why? Did you catch dengue? Outcomes?

[short-Timer]

24 minutes ago, NanLaew said:

 

Why? Did you catch dengue? Outcomes?

To prevent Dengue. That's what the vaccine is for. Outcomes? No side effects, no dengue. 

[JackGats]

5 hours ago, GroveHillWanderer said:

On the other hand, the paper also states that the data on risks for seronegative individuals for DENV3 and 4 is limited, precisely because infections with those serotypes is less common. That seems to be true for Thailand also. 

 

"In Thailand, DENV-2 and DENV-1 are the most common dengue serotypes, although DENV-3 and DENV-4 also circulate. Studies in Southern Thailand and other regions have shown DENV-2 as a dominant serotype in some years, followed by DENV-1, DENV-3, and DENV-4."

 

Epidemiology and costs of Dengue in Thailand

 

https://pmc.ncbi.nlm.nih.gov/articles/PMC9810168/

 

So it seems as though the risk of getting DENV3 or 4 is lower that for the other two serotypes.

What I'd like to know is the following: is the high protection (80%) against hospitalisation also valid for seronegative individuals, or does this figure conflate seronegatives with seropositives? If the vaccine does nothing to protect seronegatives from severe illness, or puts them at slightly more risks than non-vaccinated, better wait till you've had dengue once before getting vaccinated.

[GroveHillWanderer]

On 4/23/2025 at 5:35 PM, JackGats said:

What I'd like to know is the following: is the high protection (80%) against hospitalisation also valid for seronegative individuals, or does this figure conflate seronegatives with seropositives? If the vaccine does nothing to protect seronegatives from severe illness, or puts them at slightly more risks than non-vaccinated, better wait till you've had dengue once before getting vaccinated.

The efficacy rates given in the WHO position paper I linked to earlier listed the figures for both seropositive and seronegative individuals, and for both infection and hospitalisation, for all four serotypes.

 

Those figures are as follows (VCD stands for virologically-confirmed Dengue):

 

Quote

When stratified by virus serotype and baseline serostatus, 57 months after the first dose, the efficacy against DENV1 VCD was 56% in seropositive subjects, and 45% in seronegative subjects. Efficacy against DENV2 VCD was 80% in seropositive subjects, and 88% in seronegative subjects; against DENV3 VCD it was 52% in seropositive subjects and -16% in seronegative subjects; and against DENV4 VCD, 71% in seropositive subjects and -106% in seronegative subjects.

 

Against VCD requiring hospitalization 57 months after the first dose, efficacy was 67% in seropositive subjects and 78% in seronegative subjects for DENV1; 96% in seropositive subjects and 100% in seronegative subjects for DENV2; and 74% in seropositive subjects and -88% in seronegative subjects for DENV3.

 

For DENV4, cases numbered only 3 among seropositive subjects and 1 in seronegative subjects in the placebo group, compared to none in the vaccine group. This did not provide adequate power to estimate efficacy against DENV4 stratified by baseline serostatus.

 

So depending on which serotype you're taking about, the vaccine is up to 88% effective against infection and up to 100% effective against hospitalisation, in seronegative individuals.

[JackGats]

3 hours ago, GroveHillWanderer said:

 

 

So depending on which serotype you're taking about, the vaccine is up to 88% effective against infection and up to 100% effective against hospitalisation, in seronegative individuals.

Except for type 4: "For DENV4, cases numbered only 3 among seropositive subjects and 1 in seronegative subjects in the placebo group, compared to none in the vaccine group. This did not provide adequate power to estimate efficacy against DENV4 stratified by baseline serostatus"

[GroveHillWanderer]

1 hour ago, JackGats said:

Except for type 4: "For DENV4, cases numbered only 3 among seropositive subjects and 1 in seronegative subjects in the placebo group, compared to none in the vaccine group. This did not provide adequate power to estimate efficacy against DENV4 stratified by baseline serostatus"

I said, "up to" those figures, depending on serotype. Which is accurate.

 

The figures for DENV4 in seronegative individuals could not be determined but based on the figures for their seropositive counterparts, would almost certainly be less than 88% for VCD and less than 100% for VCD requiring hospitalisation.