West Nile Virus Vaccine: The Rush
for a Cure
Presently, there exists a vaccine for the West Nile virus
in horses, but no vaccine has yet been developed for the West
Nile virus in humans. The West Nile virus is a rapidly spreading
health problem; hence, scientific efforts into creating a
vaccine for it have been accelerated in recent years.
West Nile Virus Hot Spots
Both Central and South America are major hotspots for this
virus as they harbour significant numbers of the mosquito
population. A complex network of interaction between the virus,
the birds, and the mosquitoes exists, and it is still somewhat
poorly understood. In order for the West Nile virus vaccine
to be created, it is imperative for scientists to fully disentangle
and comprehend the inter-connections. In 2006, there were
4,269 cases of West Nile virus reported, of which 177 were
recorded deaths in the U.S.
Where to Begin
Many factors must be considered and many questions are still
unanswered. Research on a vaccine against the West Nile virus
must include the following:
- Determination of how the virus replicates and spreads
throughout the human body.
- Investigation into how the immune system reacts to the
most serious form of the virus, West Nile encephalitis.
- Examination of the environment and the yearly maintenance
of the disease.
- Comprehension of how genetic variation affects the virus
and the disease.
In 2003, the West Nile virus had a greater impact on the population
than in previous years. This fact prompted Acambis, a biotechnology
company based in Massachusetts, to begin the first human clinical
trials for a West Nile virus vaccine. The Acambis vaccine
contains genes from two different viruses, yellow fever and
Researchers at Acambis replaced some of the yellow fever genes
with genes of a surface protein for the West Nile virus. The
Acambis vaccine entered human clinical trials after performing
well with mice, hamsters, monkeys and horses. In May 2005,
Acambis, with its ChimeriVax technology, successfully completed
Phase I of their research, whereby 30 healthy adults received
a high dose of ChimeriVax-West Nile vaccine, 15 received a
low dose, and 30 control subjects received a placebo.
The study indicated that 96% of the high-dose group and 100%
of the low-dose group developed West Nile neutralizing antibodies
28 days after the initial inoculation. In December 2005, Acambis
announced its move into Phase II, and September 2006 brought
an announcement outlining very promising results. The trials
involved testing the safety, tolerance and immunogenic qualities
of the West Nile virus vaccine on healthy adults aged 18-40.
The primary purpose of this particular trial was the seroconversion
rate or the percentage of candidates who developed neutralising
antibodies at a titre of at least 1:10.
Results indicated that over 97%
of subjects seroconverted in 28
days after one single dose of ChimeriVax-West
Nile. Ongoing trials are being performed
on healthy, older adults who are
most at risk of experiencing severe
symptoms resulting from a West Nile
Article written by Anna DeGaborik
Anna DeGaborik is the author
for the All Mosquito
Netting Info website. She studies insect diseases and
prevention, specializing in mosquitoes.