The Debate About Vaccines

By Amy Fernandez

Vaccines never fail to trigger hot debates that predictably reach an incendiary point when flu season rolls around. We’ve been suspicious of them ever since Edward Jenner proved that exposure to cowpox induced immunity to smallpox. No one quite understood how or why it worked back in 1798. But this simple solution offered mankind’s first weapon against a disease that routinely killed 40 percent of its victims and left survivors scarred or blind. Rather than celebrating this medical miracle, religious, scientific, and political objections to vaccination sprang up overnight.

Over the next 200 years, vaccines neutralized many infectious diseases, most notably the eradication of smallpox in 1980.  Despite their undisputable benefits, they have never been universally accepted. They have been linked to enough problems to fuel ongoing controversy, which inevitably carried over to pets.

Reactions associated with dog and cat vaccines range from temporary pain, swelling, fever, and lethargy to far more severe, sometimes fatal, side effects. Possibly the most notorious was allergic uveitis, or blue eye, caused by an early version of canine adenovirus vaccine. Anaphylaphtic shock remains the most dreaded reaction. It’s generally linked to killed vaccines. Modified live vaccines are suspected causes of several allergic and autoimmune disorders. The list goes on, as does research to refine protocols, methods of administration, and safer, more effective versions of common vaccines.  Recombinant and DNA vaccines and non-refrigerated preservation methods are just a few promising developments in the works.

Arguably, vaccines have worked too well.  Today it’s not unusual to forego them in order to avoid potential side effects. Typically, this is rationalized by the fact that many of the highly contagious, often fatal diseases have become rare in developed countries. We can thank herd immunity for keeping them at bay. Unfortunately, this safety net is frequently mistaken for natural immunity or eradication. Canine killers like distemper, hepatitis, or rabies are a distant memory simply because herd immunity keeps them at bay.

Overall, that’s true for many human and canine diseases, but it appears to be changing.

For instance, whooping cough (pertussis) has been on the rise for decades due to resistance towards the vaccine.  So far three outbreaks have qualified as major epidemics, despite the fact that vaccination rates increased after a new purified antigenic acellular version was introduced in the 1990s. Recurring outbreaks since then were initially attributed the new version’s shorter duration of immunity. But a recent study highlights the ongoing risk/protection tradeoff of this deal.

New evidence suggests that recently vaccinated individuals become asymptomatic carriers, capable of spreading the infection to the growing unprotected population. This is not the only vaccine-preventable disease that seems to be making a comeback.

Every population includes a percentage of unvaccinated individuals for various reasons. Despite that, the protection provided by herd immunity prevents these diseases from gaining a foothold. However, if the ratio of vulnerable individuals exceeds the threshold point it will tip the balance and compromise herd immunity. Depending on the disease, 75 to 95 percent of the population must be vaccinated  to prevent outbreaks of contagion.

Historically, poverty has been the primary reason for this.  But several studies indicate that a secondary unvaccinated group is steadily contributing to these numbers for both human and canine populations. That seems to be tipping the balance.  Although no outbreaks have yet qualified as epidemics, sporadic outbreaks of leptospirosis and parvovirus are documented annually.

Potential vaccine reactions remain a valid concern. However, they pose a minor risk in contrast to the morbidity and mortality rates formerly encountered from these diseases.

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Posted by chesliepickett on Dec 30 2013. Filed under Current Articles, Featured. You can follow any responses to this entry through the RSS 2.0. Both comments and pings are currently closed.