As someone else said, lepto can cause allergic reactions in a lot of dogs. We have two combination shots, one with lepto and one without for that specific reason.
We do not give the shot to any pup under 8 weeks of age. But after that, they get it unless the owner refuses.
There was quite a major Lepto outbreak all across the US a few years back and it included humans in its path.
People have to be careful because none of these diseases just disappeard, but rather with the amount of people vaccinating against their are just fewer reported infections (much fewer). But when a whole lot of people stop vaccinating, then the disease is going to make a comeback in terms of reported infections.
In 2007, we treated 8 cases of Lepto. Maybe not too high a number for some to reconsider vaccinating for it, but only 1 dog survived. And the fact that it can be spread to humans doesn't exactly make me all happy to have to treat a dog with something that I can catch yet I wouldn't have been put at risk if one had just vaccinated for it.
(Of course I understand vaccination contraindications so don't jump on me for my opinionated comments
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And GO, correct me if I'm wrong, but Fort Dodge now produces a vaccine that protects for 4 strains of the disease over the previous standard of 2.