Malaria is a preventable and curable disease.
But it still kills one child every two minutes, overwhelmingly in Africa.
Today, the World Health Organisation (WHO) has announced it is backing a malaria vaccine for the first time.
Clinical trials have proven that Mosquirix prevents three in every 10 cases of serious malaria disease in young children.
While that may not compare with the levels of efficacy seen in the recently-developed coronavirus vaccines, malaria is so widespread and so deadly, that any layer of extra protection is welcomed by scientists.
Here Sky News looks at what malaria is, how it spreads and what is being done to prevent it.
What causes malaria?
Malaria is the serious, often deadly illness caused by the Plasmodium parasite.
The parasite is found in infected female Anopheles mosquitoes and can be passed to humans if an infected mosquito bites them.
Although there are more than 400 species of Anopheles mosquito, only five types of the Plasmodium parasite can cause malaria in humans.
They are:
Plasmodium falciparum
This is the most common type of malaria, responsible for the most deaths worldwide and is mainly found in Africa, where the disease is most prominent.
In 2018, this parasite caused 99.7% of malaria cases in Africa, 50% in South East Asia, 71% in WHO’s Eastern Mediterranean region and 65% in the Western Pacific.
Plasmodium vivax
This is the most common type of malaria in the Americas, accounting for 75% of estimated cases there.
It is also found in Asia.
Vivax causes milder symptoms than falciparum, but can stay in the liver for up to three years, which can result in relapses.
Plasmodium ovale
This is a fairly uncommon form of the disease, but is usually found in West Africa. It can remain in the liver for several years without causing any symptoms.
Plasmodium malariae
This is quite rare and usually only found in Africa.
Plasmodium knowlesi
This is the rarest form of the disease, only found in some parts of South East Asia.
All the mosquitos that are vectors for malaria are known as “night-biting” mosquitos as they bite humans between dusk and dawn.
How is it spread?
Malaria is spread to humans when an Anopheles mosquito infected with the Plasmodium parasite bites a human.
Humans cannot pass malaria to one another, except in rare cases where it is passed on through blood transfusions or the sharing of needles.
But a mosquito can become infected with the parasite if it bites an already-infected human, and spread the disease further by biting other people.
African species of Anopheles mosquitoes have long lifespans and have a stronger habit than others of biting humans, this is why 90% of global malaria cases occur in Africa.
What does it do to the body and what are the symptoms?
Malaria is an acute febrile illness, which means it causes a rapid onset of fever-like symptoms.
Once someone is bitten by an infected mosquito, the Plasmodium parasite enters the bloodstream and travels to the liver.
The infection then develops in the liver before re-entering the bloodstream and invading red blood cells.
Parasites are then able to grow and multiply in red blood cells, which cause them to burst at regular intervals – usually every 48 to 72 hours.
Every time red blood cells burst, the patient will suffer an episode of fever, chills and sweating.
The first symptoms, which also include headaches, tend to appear within 10 to 15 days of the mosquito bite.
But if malaria is not treated in the first 24 hours of symptoms, it can become extremely severe and potentially fatal.
Children with severe disease then start to suffer symptoms such as anaemia, breathing difficulties or cerebral malaria, which is when the infection spreads to the brain.
In adults, serious malaria disease can cause multiple organ failure.
Where is it most common?
Malaria overwhelmingly affects Africa more than any other place in the world.
According to the WHO’s latest report, there were 229 million cases of malaria worldwide in 2019, 94% of which were in Africa.
This was an increase of a million on the previous year.
There were also 409,000 deaths from the disease in 2019.
Just six countries – all in Africa – make up half of all malaria deaths worldwide.
They are Nigeria (23%), the Democratic Republic of Congo (11%), Tanzania (5%), Burkina Faso (4%), Mozambique (4%) and Niger (4%).
Who is most at risk?
Children under five years old are most vulnerable to malaria, accounting for 67% of deaths from the disease worldwide in 2019.
This is because, unlike adults in high-risk regions, they have not had the chance to develop partial immunity.
Pregnant women and people living with HIV or AIDS are also at a higher risk because their immune systems are compromised.
Adult populations in high-risk areas have been able to develop some immunity to malaria over time, but this is often only partial.
How is it being treated now?
Until now, there have been no vaccines available for malaria.
Instead, preventative measures and drugs are the only thing that can stop people developing severe malaria and dying from the disease.
The two main preventative measures used in high-risk regions are sleeping under insecticide-treated mosquito nets and carrying out indoor residual spraying.
As all the mosquitos that cause malaria bite at night, sleeping under an insecticide-treated net (ITN) can create a physical barrier and stop the insects in their tracks.
But in 2019 only 46% of at-risk people in Africa had an ITN.
There has also been a standstill in production of nets since 2016, when it emerged that no new insecticides would be available for at least five years.
The other preventative method used in prevalent regions is indoor residual spraying (IRS).
This is when the inside structures of people’s homes are sprayed with an insecticide, usually once or twice a year.
But protection against malaria using IRS is declining – standing at 2% in 2019.
The drop, in every region apart from the Eastern Mediterranean, is largely due to a forced change in the type of insecticides used – to a more expensive one – as people have begun to develop resistance to the old ones.
Antimalarial drugs, taken in tablet form, can reduce the risk of malaria by around 90%.
They work by suppressing the blood stages of malaria, which thereby prevent serious disease and organ failure.
Pregnant women and children in high-risk areas are recommended three-dose courses of tablets at regular intervals to reduce their risk of the disease.
People travelling from other parts of the world to high-risk areas will also be put on an anti-malarial drug course before they fly.
Why is a vaccine so important?
Although drugs can prevent malaria, as well as other preventative measures, these are not always widely available in high-risk areas, particularly Africa.
Malaria prevention programmes are in place across the globe, but there are still hundreds of millions of cases every year.
Vaccines are given out in high-risk areas, but they are unauthorised and unregulated.
Clinical trials of the new WHO-backed Mosquirix vaccine have proven to prevent three in 10 serious cases.
This is not a particularly high rate of efficacy, particularly when compared with coronavirus vaccines, but with the disease so widespread, it would still prevent tens of thousands of deaths a year.
Another vaccine – called R21/Matrix-M – is being developed by the team at Oxford University that developed the AstraZeneca COVID-19 jab.
Small-scale trials on young children in Burkina Faso done earlier this year prevented 77% of cases.
A larger study is now planned, but Mosquirix is currently the only vaccine approved by the World Health Organisation, which means it is the world’s best hope of eliminating malaria in the years to come.