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.
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