I’ve never considered myself real big on vaccines. Still, I rely on them to handle a huge chunk of the work I’d have to do if I didn’t have them around. Think of all the parvo pups and distemper cases alone—where would we treat them? How would we deal with the refuse, the contamination, the inevitable transmission?

That’s why I, for one, am grateful to the drug companies for doing this kind of work—in spite of the way today’s wind blows with all the acrimonious talk surrounding vaccine reactions.

Don’t get me wrong—my goal is not to indiscriminately push the plunger every six months with nary a thought as to the untoward consequences of doing so. Rather, I try to thoughtfully assign a degree of risk to a particular animal for any given vaccinatable disease and then use minimal measures to secure its safety and that of others it might encounter.

Yet in our practice, for all the enlightened three-year protocols and titers we do, reactions still happen (rare though they may be). Our latest brush with a severe vaccine reaction, however, has led to more stress, frustration and guilt than most.

Elizabeth is a four-pound Yorkie of indescribable sweetness. Six weeks ago, after sgnificant research and consultation, we began using Pfizer’s new periodontal disease vaccine. Two injections later we had two sick dogs. Both were painful all over, a vaccine reaction known as myalgia (muscle soreness). One recovered, but Elizabeth’s morphed into something even more sinister: polyarthritis.

Now Elizabeth’s joints hurt even when she’s not moving. Clusters of immune complexes are likely deposited around her joints, eliciting wincing pain when she’s not medicated with steroids. This kind of vaccine reaction is uncommon—so much so that Pfizer is having a hard time accepting that their product is the source of the reaction.

Still, the vaccine’s two for two at our place. Both dogs got sick the day after the vaccine. We sent it back. Maybe it was the batch?

For the record, we feel terrible. It’s no one’s goal to prevent significant disease by causing another. I’m sure Pfizer feels bad, too. But it's part of the landscape of trying to do better by our patients. Sometimes reactions have to occur so that we can find new ways to end animal sufering more safely the next time.

So it was that when I heard on NPR about the HIV/AIDS vaccine failures, I felt I knew just a little bit about how those researchers must feel. In this case, a trial undertaken in two separate parts of the world turned up higher rates of HIV/AIDS in the vaccinated group. It seems the vaccine sensitized the group to the virus instead of the other way around. Ouch!—that’s gotta hurt.

One thing is nursing a sick dog through (probably) six months of a painful process—the other? Knowing your vaccine made it easier for dozens of people to acquire a death sentence (in their part of the world, at least). Talk about guilt.

We all know medicine isn’t perfect. But we still have expectations when it comes to risks and rewards in medicine. That’s why vaccine reactions seem so odious to us. In spite of the severity of the drawbacks, it might even be easier to sign up for a vaccine trial when it comes to a disease like HIV/AIDS. Rabies makes sense, too. But periodontal disease? That’s what’s keeping me up at night.

No matter that I didn’t push the plunger on this case—vet medicine, along with all of us who might have administered this vaccine, is responsible for Elizabeth’s pain. We do our best but we f--- up, too. All we can do is take responsibility, handle these cases with compassion and stress out just a little more every time we set out to do better by giving anything that might make them worse.