October 18, 2017

Prevention Is the Best Medicine: Vaccines in the 21st Century

The use of vaccines dates back centuries. A look backward and forward shows how far we’ve come—and where we’re going.
By Meredith Rogers, MS, CMPP
An ounce of prevention is worth a pound of cure. Benjamin Franklin’s words ring as true today as they did in 1736, and although he was referring to fire prevention, prevention is a central tenet of immunization programs.

The first evidence of vaccination is from the Chinese, who as early as 1000 CE were inoculating against smallpox by taking powdered smallpox scabs from people with the disease and blowing it up the nostrils of healthy people or rubbing it into superficial cuts in the skin.

In the 16th century, explorers reported on nomadic herders in Africa who were performing similar variolation techniques to protect their sheep from sheep pox. Although using smallpox to immunize humans and sheep pox to immunize sheep resulted in solid immunity in both populations, postinoculation mortality was high as a result of contracting the full virulent disease instead of an attenuated version. The modern age of vaccination has its origin with Edward Jenner, who in 1796 recognized that humans could be protected from smallpox using cowpox as the inoculant, which was significantly less dangerous.

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Following Jenner’s discovery, vaccine development intensified. Although more than 1900 veterinary vaccines against at least 60 diseases are registered worldwide today,1-4 only a handful are considered core for companion animals and livestock. These vaccines are intended to protect our animals from infectious agents, be they viruses, bacteria, or parasites. However, new classes of vaccines against chronic diseases are under investigation. For example, a vaccine against canine melanoma (Oncept, Merial), introduced in the United States in 2010, was the first therapeutic vaccine for the treatment of cancer in either animals or humans.

Unlike traditional vaccines, which normally activate the immune system to protect against future disease, therapeutic vaccines activate the immune system to fight existing disease. There is even a vaccine to increase fertility in sheep that stimulates an immune response against the steroid androstenedione to decrease estrogen levels (Ovastim, Virbac; not available in the United States).

How Vaccines are Created
Another area under investigation is how vaccines are created. Traditional vaccines rely heavily on either attenuation or the killing of the whole pathogen to render it safe. With attenuated vaccines, a less virulent strain of the pathogen replicates in the host to promote an immune response, which sometimes leads to clinical signs of disease, especially in immunocompromised individuals. Inactivated (killed) vaccines cannot replicate inside an individual, so they do not cause clinical signs of disease, but some of these vaccines have been associated with sometimes severe immune-related adverse effects.

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