Are We Missing Out On the Benefits of Dengvaxia?

So I'm going to stick my head out because I feel there is a lot of confusion going around on the dengue vaccine again. This is my interpretation of the Sanofi release. For the record, I am an infectious diseases physician who deals with dengue on a daily basis. I am not a trained epidemiologist, but I do have some research expertise. I do not work for Sanofi and have never received any money from them. The reason I am speaking up is because I feel this vaccine has been demonized and that we may be missing out from very real benefits because of the uncertainty surrounding the interpretation of Sanofi's recent statement, and of the outcry following it.

First, a short recap of the events of the past few weeks: On November 29, Sanofi Pasteur announced the results of a new clinical study of the Dengvaxia vaccine, which has been used in national anti-dengue vaccination programs since early 2016: "The analysis confirmed that Dengvaxia provides persistent protective benefit against dengue fever in those who had prior infection. For those not previously infected by dengue virus, however, the analysis found that in the longer term, more cases of severe disease could occur following vaccination upon a subsequent dengue infection."

It didn't help that the Philippines was the first country to have adopted Dengvaxia for a national immunization program, or that the program was also under inquiry in Congress because of budget irregularities.

I'm not going to comment on the administrative side of the issue, but I want to take a step back, as a scientist, and look at some facts. There are some points which I think are being overlooked in this entire conversation.


1. First of all, the vaccine was not initially meant to be given to people who have never been infected with the virus (called "seronegatives", or people who do not have dengue antibodies in their blood as a result of past infection). The entire vaccine is based on the understanding that subsequent infections after the first tend to be more severe, because of a phenomemon called antibody-dependent enhancement, where antibodies from the previous infection of one type of dengue virus cause the current virus to cause more symptoms instead of helping clear it. That is why it is only for use in high-prevalence countries.

2. The dengue test kits in the market are meant for diagnosis of active dengue, not necessarily past dengue infection—the best test will be an ELISA test done in a proper hospital or research lab. This means that most of the tests done by diagnostic labs are not designed to detect past infection in someone who does not have active dengue. Therefore, there is no readily accessible reliable way for a physician to diagnose past infection in someone who does not have dengue. If the test is positive then it is useful, but if it is negative it is not certain.

Furthermore, only 1 out of 4 people who get dengue actually have clinical symptoms of fever and low platelets, so your child may already have had dengue without actually getting sick. A new test has been developed to more reliably diagnose past infection, but it will likely not be on the market for at least one or two more years.

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3. We are talking of a safety SIGNAL, not a statistically significant harm. This is why they used the words "could harm" versus "will harm" in the statement released by Sanofi. No one has died from this. But lots of people have died from dengue. You decide which is a bigger problem and if your risk of getting dengue is higher you should take the vaccine within the recommended parameters. Put another way, we are talking about definite benefit versus possible harm. 

4. Furthermore, the statement reiterated the efficacy of the vaccine up to 6 years, and this is a good thing. If you have started the series, you probably should complete it—otherwise you wont get the full benefit. We need to emphasize this because people may not complete their vaccination because of the uncertainty.

5. I agree this should not have been used immediately for mass vaccination until after SAGE released its recommendations. The DOH will have to explain their reasons for going ahead with the program, whatever they may be. However, this should not discredit the scientific evidence that the vaccine works when used correctly.


6. Let's look at the numbers, too. Based on studies in the Philippines, 90% in those ages 12 and above in the Philippines have the dengue antibodies in their blood—that means that Dengvaxia would work for 90% of the population. So if you have had at least one episode of dengue (like me), you should absolutely not hesitate to get the vaccine. The vaccine decreases the risk of severe dengue in this group of people by about 90% for sure. That's statistically significant.

The bottom line is that this is a GOOD vaccine when used correctly. Talk to your doctor if it is appropriate for you. Only you can make decisions about your health, but you need to make an informed decision.

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