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."
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.
Source: BBC News
No comments:
Post a Comment