Fighting cancer with a virus of plants: it's not a load of bull

If I ask you to think of a virus, I’m going to guess you’ll land on one of Zika, Ebola, HIV, Influenza or maybe at a push, Rhinovirus, the latter two of which you may be unfortunate enough to have recently experienced in the winter of the northern hemisphere. Viruses, and the infections they cause, are massive public health concerns, and for the most part this is what gets our attention. However, there is currently a vast amount of research going into the development of viruses as tools in the fight against cancer, and it’s some of this work I’d like to discuss in the blog post.

The work I’m going to talk about was published in the journal Nature Nanotechnology and comes from the Geisel School of Medicine in New Hampshire, USA. The published article has the somewhat striking title of “in situ vaccination with cowpea mosaic virus nanoparticles suppresses metastatic cancer.”

Let’s break that down. Our immune system has the capacity to destroy cancer cells, this is in fact one of the major hurdles a mutant cell needs to overcome in order to develop into a cancer. In order to escape the immune response, mutated cells need to develop ways in which to protect themselves, for instance, by releasing molecules that act to suppress the the immune system - in a sense, camouflaging themselves. This kind of immunosuppression by cells is nothing strange in our body, it’s part of a normal response to stop your immune system attacking your own body. However, cancer cells develop the ability, through mutation, to subvert this system to aid their own growth. As such, an idea that has starting to come to the front of cancer research is so called cancer immunotherapy; stimulating the immune response to fight against cancerous tissue, while leaving normal tissue untouched. So to break down the first part of the paper’s title, “in situ vaccination” is the idea of directly supplying something to trigger an immune response at the site of a cancer. The “something” that is being supplied into cancerous tissue in the case of this work, is cowpea mosaic virus nanoparticles.  

 

Cowpea peas

 

I’m guessing that cowpea mosaic virus isn’t something you’ve come across before (I certainly hadn’t). By way of background, cowpea mosaic virus, is a virus that infects the cowpea plant, and causes a mosaic pattern on the leaves (to state something you’d probably guessed). In this study of cowpea mosaic virus as an anti-cancer agent, the group work with “nanoparticles," which can also be called "virus-like particles." If you consider a virus particle, such as the one depicted for cowpea mosaic virus (below), that 3D shape is made up by very few proteins. A virus structure is essentially just a protein case for the genetic material. A virus-like particle is simply just this casing with nothing inside (literally a shell of it’s former self). Without the genetic material, these particles are no longer able to infect cells. An analogy for this could be a laptop that has had all of the internal circuit boards removed. From the outside it still looks like a laptop, but try and turn it on, and nothing will happen. Virus-like particles are of very little danger because they cannot infect cells, however, the immune system isn’t able to detect this. The cells of the immune system only ever see the outer casing of a virus and treat this as a threat - thus virus-like particles can stimulate an immune response just like a real virus (from the outside a laptop without circuit boards still looks like a laptop). And this is the basis of some vaccines, most notably of which is the vaccine against human papillomaviruses, which some readers may have received. 

 

Cowpea mosaic virus structure (from Wikipedia)

 

We can now get to the meat of the paper. To jump to the punchline, the group were able to show that injecting mice with cowpea mosaic virus-like particles could stimulate an immune response, that resulted in suppression of cancers in mice. Initially the group determined that treating cells with the virus-like particles was capable of triggering an immune response in a dish, and moreover, found that this treatment didn’t cause the cells to die. The group moved on to have mice inhale preparations of cowpea mosaic virus-like particles. In mice with no tumours, this inhalation resulted in activation of the immune system, which could be detected by an increase in the number of neutrophils (one class of immune cells) in the lungs. And indeed, collecting neutrophils from these mice showed that the virus-like particles had been taken up into these cells, thus activating them - the neutrophils treated the virus-like particles as a true threat and attempted to remove them. Importantly, this inhalation of the virus-like particles to healthy mice didn’t cause any adverse side effects or damage to the lungs.

The next experiment was to give the virus preparation to mice with tumours. It was found that before the inhalation, the immune cells in the lungs of these mice was very different to that of healthy mice. There were far more cells associated with immunosuppression (as a result of the cancer). Upon giving virus-like particles by inhalation to these mice, it was seen that there was a large increase in the number of activated immune cells capable of tackling cancer (again, a large increase in the number of neutrophils, for instance). So far then, everything seems to be going to plan for using cowpea mosaic virus to activate an anti-cancer immune response.

Next, the group started to give mice injections of the virus-like particles instead of allowing them to inhale. They found that injecting mice with cowpea mosaic virus-like particles resulted in a decreased number of tumours in the lungs. Importantly, the researchers nicely demonstrated that this reduction in tumour number was due to an immune response but using mutant mice that don’t have a functional immune system - these mice showed no change in their tumour burden.

The tumours that were being tested to this point were melanomas growing in the lungs. But it wasn’t just melanomas that showed sensitivity to the immune response triggered by cowpea mosaic virus-like particles. In one set of experiments, mice were injected with cancerous tissue in their fat pads, which then spontaneously metastasis to the lungs 16 days later. The mice given injection of virus-like particles all showed delayed onset of lung tumour formation, and survived the treatement. Similarly, mice with tumours in their colons could also be protected by treatment with the virus-like particles. 

Finally, the group tested whether injections of virus-like particles could protect against melanomas growing in the skin. Once again, they found that cowpea mosaic virus-like particles could protect the mice, and half of the mice injected completely cleared their tumours after only two injections of virus preparations. Moreover, this anti-tumour immune response was found to be long lasting, since when mice that had previously cleared tumours were injected with more cancerous tissue at a later date, 3 out of 4 completely rejected the implanted cancer (while this cancer grew in all non-vaccinated mice). 

Overall this work has nicely demonstrated the potential for the use of cowpea mosaic virus-like particles in the battle against cancer. These virus-like particles could be tolerated in mice and were seen to trigger an immune response, which resulted in clearance of cancerous tissue. The virus-like particles showed no major side effects, and even seemed to provide long lasting immunity against the cancers used in the work. The next step for cowpea mosaic virus will probably be to test safety in humans. It will take a long time, and many more studies, but perhaps a virus that infects plants could one day be used to treat cancers in humans.

From nowhere to everywhere - Zika virus

It seems to have come out of nowhere, and spread like wildfire. A new virus is rampaging through Brazil and parts of the Americas, and causing major global concern. Just as Ebola finally subsided in Africa, enter Zika virus from left stage. I’ll be honest, until a couple of weeks ago, I’d never heard of Zika virus, and I’m probably not alone. So I’ve decided to put together this blog post to discuss some aspects of this virus and the current outbreak. 

 

Countries where Zika virus has been found - from the New York Times

 

To being, let’s look at the virus itself: Zika virus is a member of the Flaviviridae family, which includes the much better known dengue, West Nile and yellow fever viruses, and like these is transmitted by mosquitoes. Because no-one really cared about Zika until recently, the virus has little published scientific literature. Typing "Zika virus" into PubMed (the major search engine of academic literature) yields 155 published articles, compared to the 9198 that are returned from searching "dengue virus” (at the time of posting). However, being that we know the virus family, this already tells us a lot. Like other flaviviruses, Zika is small with a genome of just 10.8 kilobases of positive sense single stranded RNA, which can encode 10 genes. The genome being positive sense and single stranded means that once it is released into a cell, the RNA will be treated just like any other cellular, protein encoding, RNA and interact with ribosomes to produce new protein. The 10 proteins that are produced by a cell following a Zika virus infection are responsible for taking over that cell and replicating the virus so it can spread new particles to new cells. Again, as with other flaviviruses, the Zika particle is small, and has one protein, the E protein, protruding on the surface. This protein is involved with attaching to a cell and responsible for the subsequent events that culminate in release of the genome into that cell. The E protein also makes up the main target for the immune system to tackle the virus. 

 

The structure of a flavivirus - from ViralZone

 

Zika virus was first identified in 1947 from a Rhesus macaque monkey which was being used as sentinel for yellow fever. At the time, sentinel monkeys were commonly used to detect the presence of yellow fever in an area since tests for viruses weren’t quite what they are today (at the time there weren’t even cell line to use in a lab to infect with the virus to study it!). This particular monkey, Rhesus 766, developed signs of a viral infection while in the Zika forest of Uganda. Blood was taken and used to inoculate mice, all of which became sick. Virus was isolated from the brains of deceased mice, but determined to be different from yellow fever - thus Zika virus was defined. The first human cases of the viral infection were reported in 1968 from Nigeria. Zika virus then remained largely undetected outside of Africa and parts of Asia, until 2007 and 2013 which saw epidemics in Yap Island and French Polynesia, respectively. 

Zika virus generally causes very mild symptoms in human infection, if any symptoms at all - only about 25% of cases are symptomatic. For that reason, little attention had been paid to it, until recently of course. The 2013 outbreak in French Polynesia was the first real indication that Zika infection could have more serious consequences than just rash, fever, malaise, and all the other general symptoms the initial infection can cause. During the outbreak, a spike in the cases of Guillain–Barré syndrome (GBS) were reported, with 73 individuals being diagnosed with the disease. GBS results from damage to the perisperhal nervous system (i.e. not the brain or spinal cord), causing rapid onset muscle weakness, and in severe cases, can result in paralysis. GBS can be life threatening since the peripheral nervous system is responsible for controlling the muscles involved with breathing and the heart beat. This coincidence of Zika virus spread and GBS was the first indication that Zika could potentially damage the nervous system.

So that brings us to the current outbreak occurring in Brazil, where once again, there appears to be circumstantial evidence linking Zika virus to damage of the nervous system - this time in the form of microcephaly in new born infants. Microcephaly, meaning abnormal smallness of the head, can be caused by multiple factors. Other infections can be responsible, such as rubella virus, cytomegalovirus or toxoplasmosis. As can poisoning of a foetus from alcohol, mercury or radiation. Mother malnourishment and diabetes may also be linked to microcephaly. In about 15% of microcephaly cases, the infant just has a head of smaller size, but in other cases, this small head is connected with poor development of the brain which can result in developmental delays, intelligence deficits and hearing loss, as well as premature death.  

 

Microcephaly - from Wikipedia

 

In the previous paragraph you may have noticed my wording that there is circumstantial evidence linking Zika virus to microcephaly cases; it is not clear that Zika infection is responsible. However, as Zika has begun to spread in Brazil and parts of the Americas, there has been a phenomenal spike in the number of microcephaly cases. Until 2014, there were around 150-200 cases of microcephaly in Brazil each year. The birth index for Brazil is estimated at 14.72/1000 population, in a country of around 200 million, this means just under 3 million as an estimate for the number of births in Brazil each year - so cases of microcephaly were rare. However, in 2015, there were nearly 3000 microcephaly cases, with the vast majority of these being reported in the latter part of the year, right around the time Zika virus cases started to become more common.

As I’ve stated, it is still not clear that Zika virus is responsible for the rise in microcephaly cases, though it is clearly the major culprit. More time is needed to follow pregnant women and determine if they become infected with the virus during their pregnancy. However, there will still be difficulties to determine if Zika alone is responsible. The best way to confirm a Zika virus infection is to look for the viral RNA genome in the blood of patients, however, the time in which this can be done is limited to the first week of infection. After that, diagnosis relies on finding antibodies against the virus in a patient’s blood. However, these serological tests are complicated by the fact that antibodies against Zika virus can cross-react with dengue virus - making it difficult to tell which virus was truly responsible for the presence of those antibodies. That dengue virus is endemic in Brazil, and the vast majority of people are positive for antibodies against dengue, compounding the issues with truly detecting Zika virus. However, with studies now aimed at determining if Zika virus is truly responsible for microcephaly, pregnant women will be tracked much more carefully, therefore raising the prospects of being able to catch an infection in the first week where viral RNA can be used to confirm a Zika virus infection.

Finally, what can be done? The short answer is not a great deal. We currently have no antiviral drugs to tackle any flavivirus infection, let alone Zika. Work is under way around the world trying to find broad-spectrum antiviral drugs that could be used to combat infection from multiple viruses, but whether a drug intervention would be of much use in a disease that generally causes few symptoms, except in pregnant women who may be unable to take the drugs, remains unclear. A better prospect would be the development of a vaccine, but we are a long way from that. Vaccines to Ebola were starting to undergo trials towards the end of the recent West Africa outbreak, but these had been years in the making through research on Ebola. Very little study has gone into Zika virus and potential for vaccines against it. However, there is a vaccine against yellow fever virus, and one idea would be to modify this to have the E protein of Zika, instead of yellow fever. The yellow fever vaccine is one of the best vaccines we have developed, but generating a Zika vaccine, and testing it, will take many years. Making things worse is the ethical issues of testing the vaccine in the population that seem most at risk from Zika virus, pregnant women. 

 

 

For the time being, our best option may be to tackle the mosquitoes which transmit the virus. There are the basic measures of wearing clothes to cover the skin and the use of bed nets when sleeping. Additionally, clearing standing water pools, such as in flower pots, or the inside of old tires, where mosquitoes lay their eggs will help to disrupt the mosquito life cycle. And in terms of more complex measures, many tests are under way to release genetically altered male mosquitos which cannot produce viable offspring. Additionally, work on the bacteria Wolbaccia may still hold hope for reducing the risk posed by mosquitoes (this is something I’ve previously posted on). Tackling mosquitoes seems to be one of the biggest challenges we face in the coming years. The Aedes species, responsible for transmitting Zika virus also transmit dengue virus and Chikungunya virus. The Culex species transmit West Nile virus, and the Anopheles species transmit malaria. Along with global warming, the habitable zones of these mosquitoes will spread, putting more people at risk. The best way we can tackle the dangers posed by mosquitoes is through continued scientific research, both on the mosquitoes themselves, and the viruses they harbour.

The most pressing issue now for Zika virus is determining that it is indeed the virus that is causing microcephaly, and finding ways to tackle its spread by mosquitoes. 

Hate mosquitoes, this work will help you avoid them

My two most recent posts to this blog have had an, admitted unplanned, theme of looking at viruses spread by Aedes mosquitos (Dengue and Chikungunya). Shortly after posting my last article, research was published which analysed the global distribution of the two Aedes species responsible for spread of these, and other viruses. So it seemed like a logical way to conclude this mini-series of posts. (I highly recommend going to the hyperlink for the paper as there are some cool maps to look at at the bottom).

Aedes mosquitoes are limited to where they can live by multiple factors, predominantly temperature and rainfall. The insects need high temperatures, but also need rainfall as they lay their eggs in water. These factors help to limit the habitable zone of Aedes largely to the topics. However, with global warning, the regions in which the mosquitoes can survive and spread is increasing, causing concern about the viral diseases they can transmit.

The study, which was published in the journal eLife, aimed to establish models to predict the global regions that Aedes egypti and albopictus could live. The models were based on real world data gathered by capturing mosquitoes across the globe. In total, 19,930 A. egypti and 22,137 A. albopictus mosquitoes were captured. Most of these were captured in Asia, 60% of the A. egypti and 75% of the A. albopictus captures. The Americas came in a comfortable second for the highest proportion of captures. This suggests that most of the mosquitoes currently reside in tropical parts of Asia and the Americas. Building on this knowledge, and factoring in climactic conditions that impact mosquito survival, models were generated to predict potential areas that the mosquitos can live.

Using these models, we now have more information about areas that could be at risk of the viral diseases carried by the mosquitoes. For instance, Mexico is predicted to have ideal conditions for the two mosquito species, even though none were captured there during the course of the study. In Europe, captures suggested that Greece and Italy have an increasing presence of the mosquitoes, and that while none were captured there, Spain, Portugal and much of south-eastern Europe have good conditions for spread.

A large part of this work is predictive, but it is based on a lot of data both on capture of mosquitos and climactic conditions. The knowledge that has been generated about current regions in which the mosquitoes spread, and the regions with potential, will direct public health work. Keeping an eye on whether the mosquitoes become established in Spain for instance, will help people take better precautions and look to limit the spread of viral diseases such as Dengue and Chikungunya. Forewarned is forearmed as they say.

Chikungunya - don't be scared, but do know about it

Chikungunya virus and it's beautiful symmetry

In my previous blog post I discussed advancements towards a vaccine against Dengue virus. I’ve decided to keep with the topic of viral infections that, along with global warming, are now spreading out of the tropics and causing concern. The topic this time is Chikungunya virus. My hope for this post is to tell you a little about a virus you’ve probably never hear of, but if you take nothing else from it, you’ll at least be able to pronounce the name - chihk-uhn-guhn-yuh.

The habitable zone in which mosquitoes can survive is spreading because of global warming, and this is starting to pose some serious public health issues. Chikungunya was first described in 1952, and until recently, has been predominantly confined to Africa and parts of Asia. Yet as Aedes mosquitoes, the vector for the virus, spread, so too does the disease, which has now been found in the Americas and even parts of Southern Europe. Estimates suggest there have been over 3 million cases globally.

The virus is typically carried by the Aedes aegypti mosquito whose geographical range is restricted to the tropics. However, in 2005, a new strain of Chikungunya was found with a single mutation to one of the proteins exposed on the surface of the virus that allowed it to replicate efficiently in the closely related Aedes albopictus mosquito species. This mutation, and change of vector, was responsible for an outbreak on the island of Réunion, in the Indian Ocean, that caused around 266,000 cases (in a population of 800,000). A. albopictus can survive in more temperate conditions that A. aegypti, meaning this stain of the virus poses a real thread of widespread transmission. Indeed, this mutation is likely responsible for the emergence of cases in Southern Europe.

Global outbreaks of Chikungunya (https://www.sciencenews.org/article/chikungunya-move)

More recently Chikungunya has made its way to the Caribbean and the Americas, causing nearly 800,000 cases of disease across Caribbean islands last year. Fortunately, the virus that was transmitted across the Atlantic was not capable of spread in A. albopictus, which probably played a big part in limiting spread of infections to Florida and no further into the USA. However, the fact the virus is circulating causes concern; should mutations occur allowing spread in A. albopictus, much of North and South America will be at huge risk from endemic Chikungunya spread.

Chikungunya rarely causes fatal disease (probably explaining why not many people have heard of it), however, there are no current treatment options, nor a vaccine. While the infection may not be life threatening, that isn’t to say it’s pleasant. The disease begins like may viral diseases, causing the “flu-like” symptoms of fever, headache, chills etc. However, Chikungunya can also cause severe, even debilitating join pain, which can persist for months to years. Indeed, the name derives from a word in the Kimakonde language of East Africa meaning “to be contorted,” in reference to the appearance of infected individuals. Such symptoms can put real strain on working communities, and there are reports of whole towns coming to a stand-still because of bed-ridden Chikungunya sufferers.

Chikungunya is a virus that is currently sat on the brink of major global spread, yet I’m guessing most people have never heard of it. Should the virus currently found in central parts of the Americas mutate to spread in A. albopictus, a huge number of people will be at risk of a severely debilitating disease. It does seem that infection with Chikungunya can provide protection from re-infection, making the prospects of a vaccine promising. However, as was highlighted with the recent outbreak of Ebola, without proper forward planning, and funding, science is largely reactive; should Chikungunya spread really take off, I suspect we will not be ready for it. Even though it may not make the headlines as much as other viruses, research into understanding Chikungunya is necessary. Hopefully this blog has helped illustrate why it’s important to work on viruses other than those that always hit the headlines.

Maybe one less thing to worry about from a mosquito bite - prospects of a Dengue vaccine

Under the assumption that a majority of the readers of this blog are from the UK, I’m guessing not many have experienced, or even come across Dengue fever, or “breakbone fever” as it is often referred to. Any readers from the USA, central America, Australia, or other parts of the tropics are potentially acutely aware of the disease. The illness is characterised by high fever, malaise and bone/join/muscle pain which can be crippling (hence the colloquial name of breakbone fever). In extreme cases, Dengue can present with hemorrhagic fever (similar to the symptoms of Ebola).

Aedes mosquito

Dengue fever is caused by Dengue virus (DENV for ease), which is transmitted by Aedes mosquitoes. As with other mosquito borne diseases, due to global warming, the cases of Dengue fever are increasing because the habitable zone of the mosquitoes is expanding. Currently it is believed that 2.5 billion people are at risk of DENV infection. Currently, there are no approved drugs to directly tackle DENV, nor is there a licensed vaccine, even with intense research in the area. However, recent trials of a potential vaccine, produced by Sanofi-Pasteur have been very promising, and it is this which I will discuss here. I’d first like to tell you a little bit about DENV to explain why producing a vaccine has been so challenging, before looking at the results of the recent clinical trials and the potential for a licensed Dengue vaccine.

An image from http://www.healthmap.org/dengue/en/ of the cases of DENV in that last 3 months. Areas closer to red being those with most cases and most confidence.

DENV is a very interesting virus because of its interplay with the immune system. Let us use the example of measles virus to explain what I mean. When measles virus infects an individual (or they receive the vaccine), the immune response is activated and will produce antibodies specific to that virus. These antibodies bind to the virus and block it from infecting cells and promoting its destruction in immune cells such as macrophage, stopping the infection and protecting you. Those antibodies will do nothing against any other virus, but are very effective against measles.

An antibody response is highly beneficial against certain viruses, such as measles, but the situation is a little more complex for DENV. There are four very distinct types of DENV, which are known as serotypes, DENV-1, -2, -3 and -4. Should an individual become infected by DENV-1, for instance, they will produce protective antibodies against this serotype of the virus. If someone else is infected by DENV-2, they will produce antibodies specific to that virus. Antibodies specific to each serotype are only effective for that particular virus; DENV-2 antibodies will have no protective effect on DENV-1. This production of these specific antibodies is largely what dictates there being four DENV serotypes.

If an individual is infected with DENV-1, they will produce protective antibodies against re-infection by DENV-1. However, if that person should become infected by any of the other DENV serotypes (let’s use DENV-2), this can produce a life threatening situation. The antibodies specific to DENV-1 from the primary infection will bind to DENV-2, but instead of stopping the virus from infecting cells, the antibodies will promote infection of cells that are not normally infected by DENV - a phenomenon known as antibody dependent enhancement (ADE).

A diagram to depict ADE (from http://www.the-scientist.com/?articles.view/articleNo/34586/title/Antibody-Dependent-Enhanced--ADE--Immunity/). 1) Virus infects cells. 2) The immune response is activated and antibodies produced. 3) These antibodies bind to the virus and can result in uptake to, and 4) destruction in macrophage cells. 5) Upon a secondary infection from a different serotype, 6) antibodies are release from memory B cells. 7) These release antibodies do not bind the new serotype as effectively. 8) The virus can infect more cells, such as macrophages, leading to more extensive infection.

One such example of cells more susceptible to a secondary infection are macrophage cells. Under normal circumstances, a macrophage will detect virus particles bound by antibodies and destroy them. However, in the case of DENV and ADE, the macrophage are unable to destroy the different serotype of the virus, and will instead become infected. Once infected, these cells will eventually be killed, but can also spread the virus to the rest of the body, and even into the brain. This secondary DENV infection can cause much more extensive infection, and as a result, much more severe disease, often characterised by hemorrhagic fever or shock syndrome which can be life threatening.

The case fatality for DENV is only 1-5%, yet with around 50 million infections each year, and 2.5 billion people living in areas at risk from the transmitting mosquitoes, this is still a lot of people. It is speculated that of the fatalities, a large proportion come from a secondary infection.

A vaccine is generally designed to elicit an antibody response. In short, this has been why producing a DENV vaccine has been so difficult. If the vaccine only produces an antibody response against one serotype of the virus (let’s say DENV-1), that patient is then at more risk of having a severe DENV infection than they would be without the vaccine. In order for an effective vaccine against DENV to be produced, an antibody response against all four serotypes of the virus must be produced at once, so as not to leave the individual susceptible to more severe infection. This has proved very difficult.

There have been many failed attempts at producing a DENV vaccine. However, finally it seems like there may be light at the end of the tunnel. As touched on above, the vaccine has been manufactured by Sanofi-Pasteur and it is based on the yellow fever vaccine. The first vaccine ever produced was against smallpox, credited to Edward Jenner. Once the idea of vaccination became established, the next virus on the hit list was yellow fever virus. The vaccine against yellow fever virus is still one of the most effective ever produced. Yellow fever virus and DENV are from the same virus family (the Flaviviridae), and therefore share many features. The work at Sanofi-Pasteur used the yellow fever vaccine as a backbone for their DENV vaccine (known as CYD-TDV). The yellow fever vaccine was altered to present the immune system with proteins against each of the four DENV serotypes instead of yellow fever virus, then made as a cocktail of all four (a tetravalent vaccine).

The vaccine has so far been trialled on around 31,000 children (who are at most risk of severe DENV) in South Asia and Central America and in both regions has been show to be very effective. In the South Asian trial the vaccine had 56.6% efficacy for all DENV infections, and 80.8% efficacy at preventing severe DENV infections, and importantly, showed no substantial safety concerns. While in the Central American trial these equivalent figures stood at 60.8% and 80.3%. While efficacy of around 60% may seem low, this is still a vast improvement from no protection, but most importantly, the vaccine seems to be able to reduce the number of hospitalisations from severe DENV infection by up to 80%.

The vaccine is still yet to be licensed, but with the results from these phase III clinical trials, the prospects look good. Sanofi-Pasteur has already spent 20 years and $1.7 billion in the attempts to bring this drug to market, so not least for them, but also for the 2.5 billion people at risk of DENV infection, the prospects of a DENV vaccine are highly exciting. Hopefully later this year we will see the vaccine on the market.