Malaria vaccination: Paving the way to immunity

For the first time, the world might have a vaccine for one of the world's biggest killers — malaria. 

This week, a pilot program of the new vaccine, called RTS,S, rolls out in Malawi. After the rollout, vaccination will begin in Ghana and Kenya next week. It's estimated that 360,000 children will be given the vaccine annually. 

But although it's big news, the work of malaria scientists isn't over yet. "RTS,S is the best [vaccine] we have developed so far — it shows vaccination is possible — but the efficacy is simply not good enough," Peter Kremsner, Director of the Institute of Tropical Medicine at the University of Tübingen told DW.

The vaccine, which has been developed over three decades, has shown to prevent only about 30 percent of severe malaria cases in clinical trials.

This is much lower in comparison to other vaccines, like the measles vaccine which has a 97 percent success rate. The World Health Organization (WHO) hopes to one day achieve a malaria vaccine with an efficacy rate of 75 percent or more.

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RTS,S is also limited because it's protective effect decreases considerably within four years. This is because the vaccine uses a single protein of the malaria pathogen Plasmodium falciparum (which occurs most frequently in Africa) to direct the immune system against the parasite.

However, an immune reaction to only one protein of the pathogen also means that the immune system repeatedly allows intruders to invade and malaria gets through anyway. 

In addition to Plasmodium falciparum, there are other malaria pathogens against which the RTS,S vaccine does not work.

Why do I need a vaccination?

Thousands of people still die of malaria every year. In 2017, 435,000 people succumbed to the disease worldwide, most of them children under the age of five.

More than 90 percent of malaria deaths occur on the African continent. And after widespread use of preventative treatments drove malaria cases down significantly, the World Health Organization (WHO) has reported a slight increase over the last two years.

"It seems that we have exhausted the previous methods of malaria control," tropical physician Benjamin Mordmüller, from the University of Tübingen, told DW.

"The tools we can use today don't seem to be able to provide a further reduction in the number of cases." Fighting malaria is going to require new tools — and an effective vaccine seems increasingly promising.

Read more: First new malaria treatment in decades receives green light

Why has it taken so long?

The malaria pathogen is caused by a parasite, not a bacterium or virus, as is the case with many other infectious diseases.

This parasite undergoes a complex life cycle with different stages, both in mosquitoes and in humans. This is why it's been particularly difficult to teach the human immune system how to recognize and fight the malaria parasite.

"Scientists have been trying for 50 years to isolate the individual surface structures of the malaria parasite — so-called antigens — to develop a vaccine. However, all potential vaccine candidates have failed," Kremsner said. 

An entirely different approach

Scientists at the Institute of Tropical Medicine in Tübingen have now opted for a different approach that they hope will be more successful than the RTS,S vaccine — a live vaccine in which the real pathogen is injected.

"Previously, this was not possible with such a complicated pathogen as malaria," Mordmüller, who is involved in the research project, explained.

With the support of the biotech company Sanaria in the US, the researchers have succeeded in breeding large quantities of the malaria parasite in the laboratory. These sporozoites are frozen and form the basis for the new live vaccine.

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How does it work?

In this new vaccine, which was co-developed by the Tübingen researchers, the sporozoites are attenuated with radioactive radiation before they are injected as a vaccine.

This means that the malaria pathogen can survive long enough in the human body to engender a reaction from the immune system, but dies before it can make the vaccinated person ill.

In Tübingen, this new form of malaria vaccination has already been successfully tested on healthy patients "with very high efficacy," promises Kremsner.

The advantage of this approach over the RTS,S vaccine is that the immune system now reacts to the entire parasite, not only to a single protein, which increases its effectiveness.

Who could be protected by the new vaccine?

Kremsner is certain the new vaccine will be available in a few years' time as a vaccination for travellers in malaria-prone areas. 

Currently, the researchers are trying to find out whether it could be as effective in Africa. They expect to know more at the end of this year when the initial results from an ongoing Phase II study with children in Gabon are available.

"Everything is looking very good at the moment. I would never have said that with RTS,S," said Kremsner, a tropical physician who was also involved in the approval process of RTS,S.