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The race to find an effective dengue vaccine

Published on 04/12/17 at 12:08pm

Derek Wallace, Global Dengue Program Head at Takeda Vaccine Business Unit, discusses the recent Phase 2 results showing its vaccine holds potential to become a major milestone on the road to halting the global spread of the dengue virus – a prospect that has become increasingly urgent after questions were raised over the only current dengue vaccines safety.

To begin with, could you provide me a bit of background on the latest Phase 2 results of TAK-003 (TDV)?

It was a study conducted in approximately 1,800 children aged between two and 18 years old, located in three dengue endemic countries: Panama, the Dominican Republic and the Philippines. It was an important for three reasons:

  • The first reason was that we had three different vaccine schedules: a single-dose, two doses given at three month intervals, and a single dose with a booster at 12 months
  • It was also a large Phase 2 study so that  this gave us an important safety database, in order to move into a larger Phase 3 study
  • The third aspect was that it was the first time that we had reduced one of the serotypes in the vaccine and we wanted to see the response to that reduction in the TDV2 component of the vaccine

For all three reasons, the trial was important. In terms of safety, we felt that the outcomes showed that the vaccine, TDV, had an acceptable safety profile, both in terms of general safety and tolerability – the reactor immunogenicity that can sometimes be associated with vaccine. In terms of immunogenicity, it confirmed that two doses at an interval of three months, which we’d taken forward into Phase 3, is a schedule that maximises the proportion of individuals who generate antibodies against all four serotypes of dengue. From an immunological perspective, this was important for us.

Somewhat to our surprise, we were able to identify enough cases of dengue in the study to also show that TDV also reduced the incidence of dengue in children. This, in a sense, was one of the most important findings of the study – providing a proof of concept that TDV does decrease the incidence of dengue.

As you mention, the vaccine is currently undergoing Phase 3 study – how is this progressing?

The Phase 2 is crucial for safety – we would compare the incidence of dengue in people who received vaccine against the control population, to determine a potential increase in dengue. What we found, clearly, was a decrease, which is obviously exciting. However, it doesn’t answer all of the questions that we need for a dengue vaccine.

The dengue community has learnt a lot in the last five years and we understand now the importance of prior dengue exposure in vaccine efficacy. We also understand the importance of demonstrating efficacy against each of the four dengue serotypes. The Phase 2 study we completed is too small to answer those questions, so we need to conduct a much larger one, which is our Phase 3 TIDES study. This trial is on-going in eight countries in Latin America and Asia. This has enrolled 20,000 children aged between four and 16.

Why has Takeda chosen dengue as a particular target and why is there an urgency to combat the virus?

Dengue is one of the most important vector viral forms of diseases. It is currently endemic in 120 countries globally, and there are nearly 4 billion at risk of dengue infections. Of those who are at risk, there are nearly 400 million infections every year. The burden of dengue is growing and I think that when you consider the reasons for this growth, you can predict that this will only continue into the future. The drivers behind dengue’s spread are urbanisation, climate change and globalisation, so we can anticipate that the burden of dengue will grow and the geographical spread will increase. In that context, it’s important from a public health perspective that we develop a vaccine that can be used across any age range and is able to protect people against each of the four serotypes. That’s our aim with TDV – to develop such a vaccine.

You previously worked on the first approved vaccination against dengue, Sanofi’s Dengvaxia – what was driver behind moving to work on Takeda’s vaccine?

I did work with Sanofi on the successful development of a vaccine. I’m passionate about finding a solution for dengue; TDV is a vaccine that is based upon a dengue virus – there’s an attenuated dengue-2 virus that forms the basis of the vaccine. I think that the quality of the immune response based upon on such a vaccine may be higher and more important to counter the virus.

There was a lower-than-expected uptake of the Sanofi vaccine – could you explain why this was and how this vaccine may be able to avoid such a fate?

I think it’s important to have a vaccine that can be applied widely in a community. We think that a dengue vaccine should be applicable across a wide range of ages, it should be able to be used regardless of any prior dengue exposure, and that it should be able to protect against all four serotypes of the virus. A vaccine that exhibits that kind of profile, we think, will lend itself well to implementation.

It’s too early to say whether TDV will be able to exhibit a better vaccine profile than Sanofi’s – we need to wait on the results of the larger Phase 3 studies to say. The results would have to point towards exhibiting the three factors mentioned previously: protecting against the four serotypes, being able to be used in patients with previous exposure and across age ranges.

I think it is encouraging that we’ve seen a reduction in instances of dengue in the Phase 2 study but that data doesn’t answer those key questions – so, we’re looking forward to reviewing the data from the Phase 3 trial by the end of next year.

What has been learnt by the dengue community in terms of vaccine and trial design?

Dengue is a very complex disease – it has four serotypes and those four can interact. A primary infection is unlikely to be severe – most serious infections tend to be second instances; that observation has meant that we’ve had to be very cautious in how we develop dengue vaccines, which has meant that it’s been a very slow and careful process.

We have designed our Phase 3 study to be able to assess the baseline dengue exposure in all participants – that’s an important learning we’ve applied in our clinical study design. We’ve also considered the schedule: by making decisions about the schedule we’ve chosen to move forward with, in response the immune response in the dengue naïve population. We’ve really targeted a vaccine schedule that generates antibody responses against all four serotypes in the majority of individuals. The best and the quickest schedule is the one we’ve taken forward in our programme.

On a final note, what hopes do you have for dengue treatment over the next decade or beyond?

We hope that we can provide a vaccine that can help to meet some of the public health burden of dengue – that’s our aim. We want to develop a vaccine that protects against all four serotypes, regardless of age and previous exposure to help address this increasing global health threat.

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