HEALTH - Vaccine Debate Part Three: Herd Immunity and the Future

The concept of “herd immunity” - or community immunity when talking about human populations - describes the way widespread immunity from diseases protects the entire population.

Vaccination is currently the best way to achieve community immunity, because it is the safest and most effective way to immunize the greatest number of individuals.

Mass immunization works by reducing the number of available host bodies for the infection, and it can act as a shield for individuals who are not able to receive vaccination and are therefore vulnerable.

Among the human population, these vulnerable individuals may include people with severe allergies to a component of the vaccine, pregnant people, or people who are ill.

Among the pet population, older animals, sick animals, or animals with allergies might not be good candidates for vaccination.

Mass immunization can protect these vulnerable individuals by preventing outbreaks from finding a way into the population. This is called indirect protection, and in the case of pneumococcal and Haemophilus infections in humans, indirect protection reduced the diseases among people too old to be vaccinated, and dropped the total incidences of the disease by one- to two-thirds, according to Stanley Plotkin’s “Herd Immunity: A Rough Guide.”

I = Immunized

NI = Not Immunized

Orange boxes indicate the spread of the infection, and light green boxes indicate instances of indirect protection. This chart does not demonstrate the mathematical formula for determining herd immunity threshold, but it does demonstrate how community immunity works to protect the population.

What is the result of the increase in vaccine hesitancy among parents and pet owners?

It’s tough to say, but it doesn’t look good.

Research has found that where pertussis (whooping cough) vaccination rates have declined due to vaccine hesitancy and fears about vaccine safety, rates of infection have climbed by 10- to 100-times higher than in populations that still accept the vaccine. Recent outbreaks of measles also point to the risks of reduced community immunity.

The impacts of vaccine hesitancy among pet owners are much harder to track.

Pet owners are not required to vaccinate their pets, vaccine refusals are not tracked or monitored in pets like they are in children.

A study looking at the 1991 outbreak of canine distemper in Copenhagen found that the majority of infected dogs were not vaccinated. Distemper is a serious and highly contagious disease and widespread vaccination is one of the best ways to keep pets safe.

Vaccine hesitancy is not new, and likely not going away, as discussed in Part Two of this series.

Fortunately, vaccine science is developing in new and exciting directions.

New types of vaccines, such as live recombinant vaccines and DNA vaccines, are being developed. DNA vaccines are particularly revolutionary, have the potential to offer increased vaccine stability, and do not require the presence of an infectious agent (a concern that has contributed to vaccine hesitancy).

New vaccine delivery methods for humans include needle-free vaccines and Nanopatch technology that delivers vaccines to cells just below the skin surface.

With new outbreak prediction models available, new delivery methods, and new vaccine protocols being developed that take into account pet owner concerns about over-vaccination, hopefully levels of community immunity can remain high among people and pets.

By Tiffany Sostar

Tiffany is a writer, editor, academic, and animal lover who came late to her appreciation of pets. At 18, a rescue pup named Tasha saved her from a depression and she hasn't looked back. She has worked as the canine behaviour program coordinator for the Calgary Humane Society, and was a dog trainer specializing in working with fearful and reactive dogs for many years. She doesn't have any pets right now, but makes up for it by giving her petsitting clients (and any dogs she comes across on her frequent coffee shop adventures) extra snuggles.

HEALTH - Vaccine Debate Part Two: The Controversy

Vaccine controversies are almost as old as the practice of vaccination itself, at least on the human side of the issue.

Common misconceptions about human vaccines include the idea that the immune system may be ‘overloaded’ by multiple vaccines, that ‘natural’ immunity is better than the immunity given by vaccines, or that vaccines cause other issues, like autism.

These misconceptions lead to something researchers are calling “vaccine hesitancy,” and the World Health Organization (WHO) guest-edited a special edition of the journal Vaccine in August of last year addressing this issue.

According to WHO, vaccine hesitancy “refers to the delay in acceptance or refusal of safe vaccines despite availability of vaccination services” and it’s a big problem for global human health.

It’s also not a new problem.

(historyofvaccines.org)

Smallpox vaccination in the UK started in the early 1800's, with mandatory vaccination legislated in The Vaccination Acts of 1853 and 1867.

Two anti-vaccination Leagues were formed shortly thereafter, and their rallies and public demonstrations, including the Leicester Demonstration March in 1885, resulted in exemptions for “conscientious objectors” in the 1896 Vaccination Act.

That’s old history, but it’s a story that continues to play out today.

In fact, an overview of anti-vaccination movements over the last two centuries by the National Centre for Biotechnology Information found that the arguments haven’t changed significantly in the last two hundred years, and theorized that they likely won’t change anytime soon.

And there is a link between anti-vaccination rhetoric and vaccine hesitancy in humans, and pet owner refusal or delay of vaccines in dogs and cats.

Fears about over-vaccination, vaccine toxicity, and other issues all impact pet owners’ willingness to vaccinate their pets.

These fears about vaccination are not new in the pet world. In the early 1930's, shortly after the introduction of the canine distemper vaccine, many pet owners refused the distemper vaccine for fear of vaccine-caused illnesses and these fears echoed anti-vaccine sentiment among humans. 

Dr. Danny Joffe, National Medical Director for Associate Veterinary Clinics says, “Unfortunately, there are lots of ideas out there, and they haven’t been proven or  based on science. The one thing we can say is that dogs are living longer than they were 20-30 years ago, and the reason they’re living longer is a combination of good veterinary care, including good vaccination, and proper nutrition. We’re finding the balance between protection and over-vaccinating. The benefits of vaccinating way outweigh risks.”

And there are risks, just like with any medicine or medical treatment.

Some studies have linked vaccination to joint problems such as arthritis in dogs, and this is part of why vets have moved from vaccination every year to vaccination every three years for many vaccines.

Dr. Joffe says, “Vaccines are biological, and there can be adverse reactions to any vaccine. We’ve shifted to vaccinating every three years, and that’s a more positive way to go.”

Humans can also experience adverse reactions to vaccination, particularly immunocompromised or otherwise vulnerable individuals.

Some of the fears are entirely unfounded. For example, vaccines do not cause autism, and that controversy is, itself, a complex and challenging issue that brings up questions of autism acceptance and stigma.

Other fears are less clearly wrong, and this is where questions of public health vs. individual autonomy become relevant.

Among both people and pets, herd immunity is a critical defense against the diseases that used to cost so many lives.

Think of canine distemper, or of polio. These are diseases that standard vaccination has drastically reduced. These vaccines are saving lives and by vaccinating the majority of the population, those who are unable to be vaccinated are more safe.

Public health professionals must weigh the risk of outbreaks and epidemics in the general population against the risk of an adverse reaction in a small percentage of the population.

Part three of this series will look at the question of herd immunity among pets and humans.

By Tiffany Sostar

Tiffany is a writer, editor, academic, and animal lover who came late to her appreciation of pets. At 18, a rescue pup named Tasha saved her from a depression and she hasn't looked back. She has worked as the canine behaviour program coordinator for the Calgary Humane Society, and was a dog trainer specializing in working with fearful and reactive dogs for many years. She doesn't have any pets right now, but makes up for it by giving her petsitting clients (and any dogs she comes across on her frequent coffee shop adventures) extra snuggles.