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 hot spots 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 West Nile.
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 neutralizing 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 virus infection.