Merial’s new Recombitek vaccine for West Nile gave equine vaccines an overdue quantum leap out of the dark ages. Prior to it, injectable vaccines in wide use relied on killed viruses.
Killed-virus vaccines were an improvement over live or attenuated-live vaccines because they can’t cause an infection in the animal or environment. However, killed-vaccine protection is weaker than that from actual exposure to the live viruses, whether by natural infection or live vaccine.
Recombitek uses a recombinant technology. These vaccines use a live virus that can’t produce disease in the vaccinated species. With Recombitek, it’s canarypox. The harmless virus is modified by inserting DNA from the West Nile virus into the canarypox DNA. As a result, the canarypox virus carries specific protein sequences on its surface that mimic those on West Nile viruses. When the vaccine is given, it triggers the horse’s immune system to mount an antibody response against both canarypox virus and West Nile simultaneously.
Killed-virus vaccines and recombinant vaccines work similarly in mounting an immune response. However, with the recombinant vaccine, the canarypox virus can actually enter the horse’s cells and trigger a T-cell immune response. Killed vaccines produce little, if any, T-cell response because the killed viruses can’t enter cells. The T-cell immune response is important because once it’s stimulated it can to jump into action immediately, faster than other immune responses.
Recombinant DNA vaccines are in wide use in dogs and people. In fact, the human West Nile virus vaccine, which is expected to enter final trials this year, uses the same technology. These vaccinces show:
• Stronger immunity
• More rapid induction of immunity
• Longer-lasting immunity
• Fewer side effects
As with any new vaccine, the safety and efficacy under real-life conditions remain to be seen, but we would anticipate them to be high.
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