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Monday, January 30, 2012

Vaccine Duration In Cats

Here's a question from Madeline....

My two cats come in annually to the vet for an exam and booster shots. In 2011, when it was time to have their annual, one of my cats got some sort of stomach bug and the vets advised that they do their annual routine later as she required daily anti-biotic shots and some other injection later on (she hadn't eaten or drank water for two days at that point). Just when we were about to get their annual done, the other cat somehow injured his back and they had decided not to give him his shots. So in 2011, they missed their annual shots. I'm wondering do they need to have their shots done twice in 2012 or is taking them to their 2012 annual sufficient enough?

I already know that this one is going to open a rather large can of worms since vaccines are such a hot-button topic and there isn't a great consensus of opinion in the veterinary profession.

First of all, it's common not to vaccinate sick pets.  Honestly I think it's more anecdote and speculation than hard evidence, but few vets will give vaccines during an illness.  The rationale is usually centered around avoiding stressing an immune system that is already working on a problem, as well as avoiding any side-effects from immunizations that may mask effects of the illness.  Even without hard evidence, I think the reasons are valid enough that I agree with this practice.

Madeline's question isn't as simple as it may seem.  There is great debate in veterinary medicine about the duration of immunity from vaccines, especially in cats.  This discussion is not new, having been going on for about 15 years now.  There is evidence that many vaccines provide immunity for at least three years, and some argue that it may be seven years or more.  However, there have been few challenge studies performed (where you try to induce the disease in a vaccinated pet) beyond one year.  Because of a lack of hard data, the USDA has listed most vaccines as providing immunity for only a year.  Some companies have some data that shows their vaccines can last for three years, though this can't go on the labels because they don't have government approval to say so.  Why not?  Such studies cost lots of money to perform, and the benefit of being able to change the duration on the label doesn't outweigh these costs.

Some veterinarians and immunologists are adamant that our current vaccines give immunity for 7-10 years.  However, there has been very little actual data provided, and most of the argument is based on rationalization related to how the immune system is supposed to work, as well as antibody titers.  For every specialist and immunologist that says the durations are close to a decade, there is one who says we don't have enough evidence to make such statements.  Even the specialists in the field are divided.  And titers really don't mean as much as many people think (see my discussion last year on that topic).

And to further complicate the issue, we have to look at each antigen individually, and can't make blanket statements about all vaccines.  For example, we do have good data that some vaccines for canine distemper and parvo are valid for three years.  But the leptospirosis vaccine is known to only last for one year.  Besides the antigen, the duration may vary based on the manufacturer.  And then if you throw in legal requirements for rabies we have a whole 'nother issue.

So where does this put Madeline's cats?  Honestly, a bit up in the air.  Because of these often heated debates among vets, not every veterinarian is going to do the same thing or view boosters equally.  What I say and do may be different from Madeline's vet.  Again, there is no general consensus on this topic that every vet agrees with.

Now that I've set up the background, let me give my personal opinion.  Remember, this is what I believe based on the data I've seen, articles I've read, discussions with immunologists, and conversations with the vaccine manufacturers.  I am general practitioner and not an expert, and fully realize that plenty of people may disagree with me.  But this is how I handle things in my own practice.

I do believe that many vaccines give immunity for longer than a year.  I routinely use three-year durations for rabies, canine distemper, and parvo.  With cats and the feline distemper vaccine ("FVRCP") it's a bit different because I don't think there is as much overwhelming evidence.  For cats that are high-risk and spend much of their time outside, I feel that it is important to provide the highest levels of protection and will give a duration of one year.  For completely indoor cats I will recognize the duration for three years.  I have been given support on this view by Pfizer, the brand of vaccines we carry.  

But how to booster in Madeline's case?  One thing she didn't say was when in 2011 the vaccines were due.  Was it in January and we're a year overdue?  Was it in November and we're only a few months out?  The answer does matter.  Realizing that immunity doesn't magically end on the 366th day after vaccinating, I do give a grace period.  For annual/triannual vaccines I will allow up to six months overdue and still be valid for a standard duration.  If it's supposed to be a three week booster, I'll allow up to eight weeks.  If it is beyond these periods I'll require an additional booster three weeks later to make sure that we re-stimulate immunity.  These protocols are based on discussions with specialists and vaccine companies, and are what we use.  I don't expect every vet to do the same thing.

Madeline, the best thing you can do is to talk to your vet and ask what they want you to do.  There is not one single answer to this situation and I can't say what you should or should not do in your specific case.