Malaria vaccine shows early promise in clinical trials
A malaria vaccine has shown
promising results in early stage
clinical trials, according to
researchers.
Researchers found the vaccine, which is
being developed in the US, protected 12
out of 15 patients from the disease,
when given in high doses.
The method is unusual because it
involves injecting live but weakened
malaria-causing parasites directly into
patients to trigger immunity.
The research is published in the journal
Science.
Lead author Dr Robert Seder, from the
Vaccine Research Center at the National
Institutes of Health, in Maryland, said:
"We were excited and thrilled by the
result, but it is important that we repeat
it, extend it and do it in larger numbers."
Many bites
It has been known for several decades
that exposure to mosquitoes treated with
radiation can protect against malaria.
However, studies have shown that it
takes more than 1,000 bites from the
insects over time to build up a high level
of immunity, making it an impractical
method of widespread protection.
Instead, a US biotech company called
Sanaria has taken lab-grown mosquitoes,
irradiated them and then extracted the
malaria-causing parasite (Plasmodium
falciparum ), all under sterile conditions.
These living but weakened parasites are
then counted and placed in vials, where
they can then be injected directly into a
patient's bloodstream. This vaccine
candidate is called PfSPZ.
To carry out the Phase-1 clinical trial,
the researchers looked at a group of 57
volunteers, none of whom had had
malaria before.
Of these, 40 received different doses of
the vaccine, while 17 did not. They were
then all exposed to the malaria-carrying
mosquitoes.
The researchers found that for the
participants not given any vaccine, and
those given low doses, almost all became
infected with malaria.
However for the small group given the
highest dosage, only three of the 15
patients became infected after exposure
to malaria.
Dr Robert Seder said: "Based on the
history, we knew dose was important
because you needed 1,000 mosquito
bites to get protection - this validates
that.
"It allows us in future studies to increase
the dose and alter the schedule of the
vaccine to further optimise it. The next
critical questions will be whether the
vaccine is durable over a long period of
time and can the vaccine protect against
other strains of malaria."
Malaria kills about 600,000 people each
year and infects more than 200 million
He added that the fact that the vaccine
had to be injected into the bloodstream
rather than into or under the skin made
delivery more difficult.
Commenting on the research, Dr Ashley
Birkett, from the Path Malaria Vaccine
Initiative, said: "They are clearly very
early stage trials in small numbers of
volunteers, but without question we are
extremely encouraged by the results."
He added that most current vaccine
candidates targeted parts of the P.
falciparum parasite rather than the
whole organism.
"This approach induces a broad
response against a lot of different targets
on the parasite," he said.
There are currently about 20 malaria
vaccine candidates in clinical trials.
The most advanced is called RTS,S/AS01,
which has been developed by the
pharmaceutical company
GlaxoSmithKline, and is in a Phase-3
clinical trial involving 15,000 children in
Africa.
According to the latest figures from the
World Health Organization, there were an
estimated 219 million cases of malaria in
2010 and an estimated 660,000 deaths.
