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The vaccine for animals is, frankly, not very good. It covers just a handful of serovars out of the hundreds of serovars identified; serovars most commonly reported in North America. And that coverage is not great, with some potential for infection and disease in vaccinated animals. Bacterin vaccines in general are imperfect, often requiring frequent boosters.

Which brings us to your question - the vaccine for animals wouldn't be that good in humans, either - the majority of cases in people involve one of the ~200 serovars outside of North America - Asia, Central/South America, etc.

Prophylactic antibiotics (doxycycline most often) can instead be provided for people visiting areas/participating in activities with high risk.

In short, it's a disease of developing areas (low pharmaceutical investment) that's tough to develop a broad and effective vaccine against because of the wide range of serovars, with a cheap and easy antibiotic preventative available for those who want it.

E: I did find that at least one lab is working on a universal lepto vaccine: https://elifesciences.org/articles/64166

From Wikipedia:

There is no human vaccine suitable for worldwide use. Only a few countries such as Cuba, Japan, France, and China have approved the use of inactivated vaccines with limited protective effects. Side effects such as nausea, injection site redness and swelling have been reported after the vaccine was injected. Since the immunity induced by one Leptospiraserovar is only protective against that specific one, trivalent vaccines have been developed. However, they do not confer long-lasting immunity to humans or animals. Vaccines for other animals are more widely available.

What this means is that when they try, the human immune system doesn't remember, for some unknown reason, for very long.

There is already a Leptospirosis vaccine for humans... Several have been available since 1920...

Challenge is there are many different types of leptospiral bacteria and they live in many different animals.

The current top priority is reducing infection in animal reservoirs.

The process for approval for animal vaccines and human vaccines varies quite significantly in most countries. The standards for safety, efficacy and duration of protection are lower, costs of the trials and number of trials required are lower and generally the burden is significantly less for animal vaccines. It is a large investment to have an animal vaccine approved for use in humans assuming it works in them, and even if you can use the technology to make a human effective one there remains a high risk that even though effective it will not be good enough for regulatory approval.

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The animal version of the vaccine also does not convey long-lasting immunity and needs to be boosted yearly.

You are correct! Most bacterial vaccines will not offer long lasting immunity compared to viral vaccines.

The name says it all. Leptospira is a spirochete. They look like corkscrews, and much like other spirochetes such as the lyme disease pathogen and syphilis pathogen, the little fuckers will corkscrew into your cells, hiding from the immune system. This also makes it hard for antibiotics like doxycycline to get into the "hosting" cells. Then add in the normal mutation rates in terms of outer cell wall sugars and protein shapes etc and vaccines are not as useful. So they hide from the immune system and they mutate too fast.

Piggybacking, how come with things like this and the flu with multiple strains we can't just combine multiple vaccines into one shot to combat multiple strains?

So with flu in particular it mutates constantly with old strains becoming less common and new ones we don’t have vaccines for becoming more common each year. That’s why you get regular boosters to get the latest version of the vaccine.

Sadly we can’t predict how it might mutate, and things like flu and covid mutate a lot, so we can’t make a preemptive vaccine.

For viruses that mutate slower (often because they spread slower through populations and/or are very rare), your childhood vaccination is likely to stay effective your whole life.

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Ah that makes more sense.

When they say there's multiple strains but they don't know which one will be dominant this year, it suggests theres like a finite number that remains constant and they're just guessing which one is up this year, rather than the idea of a mutating and evolving virus like we understand Covid to be.

We do actually have multiple flu strains I'm the vaccine. Most of the vaccines now are Quadrivalent, meaning they have four strains in the one vaccine. The problem is that the flu mutates quite rapidly and there are many subtypes of each of the larger virus clades, and predicting which ones will be most active each season is hard. Scaling is a bit hard because it's essentially making 4 vaccines and packaging them in one syringe, so adding more varieties has linear costs but diminishing returns.

Well, for flu we do that - the flu shot you get will target 4 different variants. And the newer covid "bivalent" boosters target 2 covid strains.

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The newer pneumococcal vaccine has 20 strains! Just a lot of different bacteria out there.

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Are all of them everywhere are they specific to certain animals other than rats? I know that the lepto vaccines are important for dogs coming into contact with rats . The shots I give my dogs only have 2 versions of lepto vaccine in them. I didn’t know there were so many. How dangerous is it to have a vaccinated dog work as a ratter in the United States?

Great question - the prevalence of various serovars in a given area can change over time, but it's rare to see an odd Central American serovar become endemic in e.g. North America - they are fairly region-specific.

As far as species-specificity - each serovar has a presumed natural reservoir, a "maintenance host". That doesn't mean that it only affects certain species, it's just that some serovars infect a host without causing severe disease. Swine serve as maintenance hosts for serovars pomona and bratislava, for example, and dogs are maintenance hosts for canicola - one of the serovars in your dog's vaccine. The other in your vaccine is icterohemorrhagiae, for which rodents serve as a maintenance host.

How dangerous is it for a dog to work as a ratter? I think that vaccinating is a good place to start, but I'd go with the tetravalent vaccine, personally. It includes serovar grippotyphosa, which also has rodents as a maintenance host, as well as pomona (cattle/pigs). Clinical leptospirosis is not super common in dogs, but dogs exposed to rodents would be at the highest risk. I had a coonhound I used to hunt with, and I would always keep her up to date on her lepto vaccine. It was somewhat common where I lived at the time - upstate NY. Cases seem to be on the rise in NYC even, with an outbreak earlier this year linked to a dog park in Brooklyn.

I wish there were a good reference for serovar distribution in the US, sounds like maybe something someone should work on. There are maps with case distribution online, but not serovar distribution.

> it suggests theres like a finite number that remains constant and they're just guessing which one is up this year

Close! Influenza is recombinant, meaning different viruses can swap out sections of genome with each other. The huge majority of viruses don't do this, and influenza is the only one that's super infectious.

You know how strains are named stuff like H1N1 or H5N8? H and N refer to the most important surface proteins, and the numbers are the specific variety. Within each variety there are tons and tons of mutation versions. So if you have an H-mutant virus and an N-mutant virus that seem to be doing well on their own, they may combine to become even more infectious. If you have two H-mutants, they are much less likely to suddenly become a problem unless they can find an N-mutation that is more infectious or more dangerous.

Note that they can also recombine with animal (eg pig or bird) strains, not just humans. It's not that it jumps species so much that it can potentially combine two dangerous aspects- the H protein may be dangerous in all species, but the N protein may be holding it back. If it picks up a human-compatible N protein, suddenly we're in trouble. We know this is how a lot of the more recent big waves of influenza happened, like H1N1.

Influenza mutates faster than covid even without recombination, but covid is SO infectious and immunity is still not widespread enough to keep up with mutations that are relatively small. Influenza is battling against centuries of built-up immunity, so it needs to be really lucky to have a sudden change.

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This is, in fact, done. Many flu vaccines are labeled "quadrivalent", which means that they provide antigens for four different flu strains. Similarly, the new (for Fall 2022) "bivalent" Covid vaccine boosters encode proteins for both the original Wuhan strain and Omicron. Gardasil-9 provides protection against nine different strains of HPV.