Melbourne researchers have found what they suspect could be a "secret ingredient" towards an effective malaria vaccine, according to a new study, with scientists hoping a similar strategy could be deployed in the race for a coronavirus vaccine.
According to the World Health Organisation (WHO), malaria infected more than 228 million people worldwide in 2018 and killed more than 405,000 — the majority of them children under five.
The mosquito-borne disease is most deadly in sub-Saharan Africa, but also impacts people living in South-East Asia and the Pacific.
Once a person is bitten by the mosquito, the infection travels to the liver first before entering the bloodstream and wreaking havoc on the body.
The research, published in peer-reviewed journal Cell & Host Microbe on Tuesday, was conducted in mice and found a way to prevent malaria from progressing from the liver, according to co-author Associate Professor Irina Caminschi from the Monash Biomedicine Discovery Institute.
"Our vaccine amplifies an army of killer cells, which then can eliminate malaria-infected cells. So it's a very different approach. And it's extremely effective," she said, explaining other vaccines work by eliciting antibody responses.
"We've identified a protein that clearly is seen by the immune system. And we can use that protein to educate the immune system that this is a malaria protein, and it is a problem — you need to destroy it.
"That was the first important discovery and it's a little bit like uncloaking the enemies and making something that is hidden before become very visible."
Will mice findings translate to humans?
Co-author Dr Daniel Fernandez-Ruiz, a postdoctoral researcher at the Peter Doherty Institute at the University of Melbourne, said mice could be protected for about 200 days, or about a third of their lifetime, though the protection wanes over time.
"Mice are very difficult to protect against malaria, so the fact that we are getting good protection at late time points after vaccination is really good, really promising," he said.
"We can expect that if we are able to protect mice against malaria, with this vaccine, one day we should be able to protect humans with a similar vaccine, but there is a lot of work that we need to do to be able to translate this into humans."
Associate Professor Caminschi said an extension of the work in malaria with the liver could have potential application for research into combatting the new coronavirus — a project she plans to tackle next.
"We are facing this world pandemic with COVID-19. This is a disease that hits the lungs very, very hard. And our vaccination strategy is actually very flexible," she said.
"With a few tricks, we can actually create protective immunity in the lung. So we can use the strategy to create killer cells that are ready and waiting for something like a COVID-19 virus to infect the lung and eliminate it before it actually takes hold."
Dr Danielle Stanisic, an associate research leader at the Institute for Glycomics at Griffith University, who has spent 20 years on malaria vaccine research and is independent of the study, said if the research could be replicated in humans, it would be a "very exciting" development.
"They've been very lucky to find an equivalent protein in the human malaria parasite," she said, adding the protein was found in the Plasmodium falciparum malaria species — the deadliest kind.
But she said scientists always had to be cautious about whether studies in rodents could give similar results when tested in humans.
"You've got to be cautious about rodent studies … That's a limitation of any sort of research — when you move from an animal model to the human model, is it going to perform the same?" she said.
"I think the real challenge for the sort of vaccine that this paper is talking about is it has to be 100 per cent effective," she added, saying that if even one liver cell failed to stop the parasite, it could infect the bloodstream.
The need for a vaccine against malaria
While a vaccine is currently being trialled in African countries by the WHO, the researchers say vaccines tested in Western countries and clinical trials can often fail in the developing world, in part due to patients' compromised immune systems.
William Pomat, director of Papua New Guinea's Institute of Medical Research, described malaria as "devastating" in the country, which had more than 488,000 confirmed cases of malaria and 273 confirmed deaths in 2017 — though the estimates were much higher, according to the WHO.
While the country had made strides to reduce its malaria infection rate over the past decade, there was a concerning spike in recent years.
"Obviously a vaccine together with other interventions that are currently ongoing will reduce malaria further. The vaccine, though, must be protective against all parasites that exist in the country," Dr Pomat said.
Dr Fernandez-Ruiz added the research was still in its early stages, that it would take time to translate into humans, and that a potential human vaccine would need to identify many more antigens — or fragments of the malaria parasite — not just the one in this study.
Associate Professor Caminschi said while drugs could be used to prevent malaria, all drugs have side-effects, making the development of a vaccine key to treating the disease.
"The other important point to make, and this is very serious, is that the parasite is evolving to acquire drug resistance," she said.
