Syringe w needleVaccination discussions can get pretty heated. It’s not as bad with animals as with humans (thanks in part to the discredited (and formerly Dr.) Andrew Wakefield). Yet, there is still a reasonable number of people who are opposed to vaccination of pets, and probably a bigger number who are wary. There are various reasons for this, but a big one is the fear of adverse effects or reactions.

No, vaccines aren’t completely innocuous. Any vaccine can cause an adverse event. It’s rare, but it’s a fact of life that when we try to stimulate the immune system for good reasons, sometimes it doesn’t do what we want. Some vaccines may pose a greater risk of causing problems, and one that frequently gets discussed is leptospirosis vaccines. The concern is based on some reasonable history, since older lepto vaccines did seem to be associated with higher rates of adverse effects (especially among small breed dogs). However, the newer vaccines are both much more effective and seem to pose a much more limited risk of adverse effects. Data now provide more support to this last statement.

A paper in the latest edition of the Journal of the American Veterinary Medical Association (Yao et al 2015) looked at records from 130,557 (yes, over 130 thousand dogs!) that did or did not have a history of lepto vaccination. Retrospective studies using medical records are always a bit dodgy because of the (sometimes poor) quality  of medical record data, but a large and well-designed study helps limit those problems. The authors looked at records from dogs that were vaccinated during their veterinary visit. They then evaluated adverse events that developed within the 5-day period after vaccination. Not all those adverse events would have been caused by vaccination. However, it’s assumed that adverse events not associated with vaccination (e.g. diarrhea caused by some other issue) would be evenly distributed among the groups. It’s likely that this approach underestimates adverse events, but realistically, it probably only missed some mild ones. If the dog developed an adverse event of any consequence, odds are greater that this would be recorded in the medical record.

The results of the study showed:

  • The rate of adverse events in all dogs was 26.3/10,000 (just over 23 dogs out of every 10 thousand had some issues in the five day period after vaccination).
  • The rate in the dogs vaccinated against lepto was 53/10,000. The most common adverse event recorded was “nonspecific vaccine reaction.”
  • The rate in dogs vaccinated against anything else was 22.1/10,000, with “non-specific reaction” again being the main adverse event recorded.
  • Some breeds had higher rates of adverse events. The “winner” was American Eskimo Dogs, with a rate of 110.5/10,000

So, at first glance, this might raise some concern, with a rate of adverse events in lepto-vaccinated dogs that’s double the non-lepto-vaccinated dogs. Even when the analysis controled for other differences between groups, such as unequal distribution of breeds, age and weight, lepto-vaccinated dogs still had adverse events at a rate of 2.13 times that of other dogs.

But, let’s make sure this is put in perspective. This would indicate that vaccination increased the risk by ~26 events/10,000 dogs. So, if you lived long enough to own 400 dogs (or if your dog lived long enough to get 400 lepto vaccinations), you’d eventually get one that developed a complication. Further, most of those were ‘nonspecific’ and presumably mild. There was no significant difference in the incidence of hypersensitivity reactions (which is the more severe and concerning type of vaccine reaction).

The authors’ conclusion is reasonable: “These data suggest that vaccination against leptospirosis should be performed for all dogs at risk of the disease except those that have had hypersensitivity reactions previously.

Lepto vaccination isn’t needed for all dogs, but if you live in an area where lepto is present, vaccination should be considered. It’s a nasty disease, and a quite safe and effective vaccine. Don’t let internet hype lead to an increased risk of disease.

More information about leptospirosis can be found on the Worms & Germs Resources – Pets page.