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It's Time: Scientists Are Getting Really Close to a Malaria Vaccine

A new candidate just proved 100% effective in clinical trials.

FIONA MACDONALD
16 FEB 2017
 

A new malaria vaccine candidate has proven up to 100 percent effective in clinical trials.

The potential vaccine introduces live malaria parasites into patients, paired with the medication needed to combat them. It was given to 67 healthy humans, and the nine participants given the highest dose were 100 percent protected against the disease for at least 10 weeks after vaccination.

 

This is only a Phase II clinical trial, aimed at looking at how well the vaccine works in a small group of healthy people, as well as testing the side effects. 

But the most exciting part is that it's not the only vaccine candidate currently proving itself in clinical trials.

Last year, the World Health Organisation (WHO) announced that a pilot programme involving the world's first licensed malaria vaccine - RTS,S, also known as Mosquirix - would be rolled out in three sub-Saharan African countries in 2018.

Mosquirix has so far only proven up to 50 percent effective in children, but it's hoped that further testing and dose tweaking in the pilot program could improve that efficacy further.

Now, another new vaccine candidate called Sanaria® PfSPZ-CVac has just cleared Phase II clinical trials. It's not as far along in the drug development process as Mosquirix, but so far, it's showing the potential to be a lot more effective. 

Regardless of which one ultimately ends up offering better protection, the reality is that after more than a century, we're finally getting really close to not just one, but two viable malaria vaccines hitting the market.

 

Malaria still kills more than 400,000 people each year - most of those in Africa - and nearly three-quarters of deaths in children under the age of five. WHO estimates that some 214 million people were infected in 2015 alone.

Being able to cheaply and effectively vaccinate vulnerable populations again the disease would save millions of lives.

But it's a task that scientists have found challenging. Malaria is transmitted by a group of mosquito-borne parasites - most infections and deaths are caused by the particularly nasty parasite Plasmodium falciparum

Previous vaccine candidates, including Mosquirix, have been designed to protect the body against this threat by introducing it to different molecules from this parasite.

The hope is that this little 'sneak preview' would be enough to get the immune system to mount a full-blown attack on the next encounter, but so far, this approach hasn't proven effective enough to offer 100 percent effective in humans.

Instead, the latest candidate to hit clinical trials has a different strategy.

Sanaria® PfSPZ-CVac is unusual, because it contains whole, live malaria parasite - not just parts of the pathogen or inactivated versions of it. 

These live malaria parasites were injected into the body of trial participants alongside medication called chloroquine, which is known to kill the parasites.

This vaccine was given to 67 healthy adult participants, none of whom had ever had malaria before. Different doses of the vaccine candidate were tested, and the best protection was seen in nine people who were given the highest dose of the vaccine three times at four-week intervals. 

Ten weeks after the trial, all nine of them had 100 percent protection from the disease. The researchers stopped actively measuring antibody response at that point, but the participants showed signs of ongoing protection after that.

"That protection was probably caused by specific T-lymphocytes and antibody responses to the parasites in the liver," said Peter Kremsner, one of the researchers running the trial from the German Centre for Infection Research (DZIF).

The liver is particularly important in malaria infection, because after someone is bitten by an infected mosquito, the parasite spreads to the liver where it reproduces before exploding back into the body and causing malaria.

During that down-time in the liver, the immune system could shut down the infection, but the parasite isn't making the patient sick as yet, so it doesn't do anything.

Current medications, including chloroquine, treat the parasite as soon as it breaks out of the liver, but in order to properly protect against it we need to stop malaria before it gets to the liver in the first place.

By injecting people with an active parasite straight into their bloodstream, the new vaccine candidate is effectively mimicking the second part of the disease, giving the body a preview of what's to come, so it can shut it down early next time.

"By vaccinating with a live, fully active pathogen, it seems clear that we were able to set off a very strong immune response," said trial leader Benjamin Mordmueller.

"Additionally, all the data we have so far indicate that what we have here is relatively stable, long-lasting protection." 

The fact that the parasite is injected alongside chloroquine also meant that participants were protected from actually developing the disease - there were no signs of adverse effects on any of the test subjects.

While the group of nine people given the highest dose had the best protection against the disease, the lower doses given to other groups achieved efficacy of between 33 and 67 percent.

But while this trial was promising, so far, all the team has shown is that the vaccine works in high doses, and doesn't cause side effects over a 10-week period. 

The next step is to test the vaccine's effectiveness over several years - which will happen in a phase III clinical trial in the African nation of Gabon that's already been planned and funded by DZIF.

Mosquirix has completed phase III clinical trials, and in 2018, will be tested on the general public by WHO.

Only time will tell how successful either of these vaccines will be in the long-term. But drug development is an incredibly lengthy and expensive process, and it seems that when it comes to a malaria vaccine, we're finally getting to the pointy end.

And that's definitely worth celebrating.

The results of the latest Sanaria® PfSPZ-CVac trial have been published in Nature.

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