My Dogster editor approached me recently. August is National Immunization Awareness Month, and he wondered whether I might have anything to say about the subject. Indeed, I have plenty to say. Vaccines have been on my mind lately.

In the history of medicine, there have been many epic steps forward. Germ theory of disease, antibiotics, diagnostic imaging (X-rays, ultrasound, MRI, and so forth) and anesthesia all dramatically changed the landscape of medicine. But when it comes to sheer numbers of lives saved and quantity of misery avoided, no advancement can come close to vaccines.

Few people reading this blog will have personal experience with smallpox. It was one of history’s most dreadful diseases. It was wiped from the face of the earth by vaccines in 1977. Similarly, few living people can remember poliomyelitis, also known simply as polio. It has been eradicated through vaccination from all but a few areas, where anti-vaccine activists are offering it safe harbor and helping it to stage a comeback.

And did you know that until modern times your best friend could cause your worst nightmare? Until the widespread adoption of rabies vaccines in the developed world, dogs were the No. 1 source of human rabies exposure. In developing countries they still are, and an estimated 25,000 to 55,000 people, mostly children, die from the horrid condition each year.

Parvoviral enteritis, also known as parvo, is an ubiquitous disease of puppies. It causes vomiting, diarrhea, sloughing of the intestinal tract, and bone marrow suppression. There is a simple rule of thumb for determining a puppy’s risk. A puppy who has been properly vaccinated almost certainly won’t contract parvo. One that has not likely will.

Vaccines are good. Period. No other invention in the history of medicine has saved so many lives so elegantly for so little money. I’m left to wonder: Why are they so controversial?

First of all, they’re actually not very controversial among people in the know. Very few immunologists, public health workers, epidemiologists, scientists, and medical or veterinary providers have many bad things to say about them in dogs and in people (cats are a slightly different story). Some of the most outspoken opponents of vaccines include a former Playboy Playmate who believes (against the evidence) that vaccines cause autism and certain folks in Nigeria and Pakistan who believe vaccines are an attempt by Westerners to sterilize their communities.

So, scientifically, is there anything bad about vaccines? It turns out that any product that has an effect on the body — whether it’s a vaccine, a medicine, or an herbal or natural remedy — has the potential to cause adverse effects. There is no such thing as a medical contrivance free of side effects, and vaccines are no exception.

Vaccines work by stimulating the immune system. This causes the immune system to prepare to resist the disease in question. When the individual later is exposed to the disease, the immune system is already warmed up and in fighting form — and the germs are suppressed before the individual gets sick.

When the immune system is stimulated by vaccines, the individual can feel a bit sick. That is why many puppies are sleepy after shots, and why I am sleepy after receiving a tetanus vaccine. Both puppies and I also may experience soreness at the site of injection. These are normal responses to vaccines.

Less frequently, the immune system can react aberrantly to vaccines. Symptoms typical of allergic reaction, such as facial swelling and hive on the body, may develop. Other uncommon and highly unpredictable reactions occur in some individuals as well (more on that next week). These reactions are generally treatable with medications that attenuate the immune system’s short term response.

Very rarely, dogs may suffer from full-blown anaphylactic shock after vaccination. This is manifested by collapse, low blood pressure, pale gums, and potentially rectal hemorrhage and death. How common is post-vaccination anaphylaxis? In 14 years as a vet I have seen it once (and the dog made a full recovery).

Many people worry that vaccinations may cause scary autoimmune diseases like immune-mediated hemolytic anemia (IMHA). And it is true that in very rare instances dogs will develop IMHA shortly after receiving a vaccine or a medication. However, I have seen no evidence that puppy shots predispose dogs to IMHA later in life.

In fact, if you are worried about the stimulation your dog’s body will receive from a parvo vaccine, I encourage you to think about the alternative: parvoviral infection. Such infections cause antigenic stimulation that utterly dwarfs that which any puppy might receive from a vaccine, or even from hundreds of vaccines.

Although I firmly believe that vaccines are good, I also believe that dogs should not receive too much of a good thing. Over the course of a lifetime there is little doubt that too many vaccines is healthier than too few. But there’s no point in giving too many.

This is why I recommend that you and your vet sit down and talk before vaccines. The quantity and frequency of vaccines that your pup needs depend on his age, lifestyle, and history. Remember that certain vets haven’t kept up with their continuing education and may not have internalized the most up-to-date information about vaccines. Find a good vet who knows his stuff and is willing to talk.

And finally, remember some rules of thumb. Vaccines are extremely important for puppies, but the frequency with which they are administered should decrease with age. Not every dog needs every vaccine. For instance, a teacup Poodle who lives almost exclusively indoors and never boards at a kennel has little need for the vaccines against Bordetella and leptospirosis. Smaller dogs are more likely to suffer acute vaccine reactions. And all dogs are more likely to suffer acute reactions if they are given large numbers of vaccines on a single day. Therefore, if you decide that your dog should get a bunch of shots, consider spreading them out by a few weeks. Finally, remember that rabies vaccination is mandated by law almost everywhere in the developed world.

I was aggressive about my pal Buster’s vaccination in his youth. However, now that he is in late middle age I’ve backed off substantially. His last parvovirus vaccine was four and a half years ago and counting, and I have no plans to repeat it any time soon. His rabies vaccine, on the other hand, is and will always remain current.

Read more recent stories on vaccines:

• On Dog Vaccinations: 9 Things to Consider
• Is the Canine Bordetella Vaccine Safe for Dogs?
• Anti-Vaccine Ignorance Is Bad for Dogs and Humans Alike

Learn more about dogs with Dogster:

• Why Do Dogs Lick People?
• 6 Ways to Thwart an Off-Leash Dog Rushing You and Your Dog
• I Worked at a Large Commercial Pet Store, And What they Do to Puppies Will Shock You

Got a question for Dr. Barchas? Ask our vet in the comments below and you might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)