The RWAF policy statement on this is as follows:
“Vaccinations are recommended as soon as possible after 5 weeks old. Vaccinations should not be given at the same time as neutering as that leaves a window of risk when the rabbits aren’t protected. Carrying out vaccinations at the same time as neutering also carries risks, both to the rabbit’s health and to the efficacy of the vaccine.”
Here is some further explanation of why this practice is not advised.
A temperature increase can occur and this can cause confusion with the post-operative monitoring of the animal as an increase in temperature could be seen as evidence of infection. Or there could be an infection that is hidden by the increase caused by the vaccination.
There are other potential adverse reactions, but those are much rarer. Acute hypersensitivity reactions leading to death are extremely rare, but could be confused with other post operative complications.
No information is available on the safety and efficacy of the vaccine when used with any other veterinary medicinal product. A decision to use this vaccine before or after any other veterinary medicinal product therefore needs to be made on a case by case basis.
This does not mean that it will cause problems if used with other drugs, it just means they have not tested its safety alongside other drugs, and cannot say one way or the other, for certain. It would obviously depend on the drug, with anything negatively affecting the immune system being at particular risk of reducing vaccine efficacy eg steroids.
“Vaccinate only healthy rabbits”
This warning is present on nearly all, if not all vaccines. Anything affecting the general health of the rabbit (which can include anaesthesia and surgery), could reduce vaccine efficacy, and neutering falls into this category.
Neutering usually takes place at 12-20 weeks so if vaccination is put off until then, there will be a window of susceptibility to the disease.
With any kind of medical treatment there are often exceptions to any hard and fast rules and decisions need to be made on a case by case basis. For example, there were rabbits where knowledgeable vets felt it best to administer both vaccination and neutering concurrently as they were animals who were very stressed by practice visits. Similarly, if the rabbit is only going to get one visit to the vet, for example a rescue situation where they are taken to be neutered, and will not be returning for follow up checks (which of course is not ideal in itself), then vaccinating at the time might be justified for pragmatic reasons. Otherwise, most practices would include 1 or 2 follow up post operative checks, which would be a better time to vaccinate, for example at 7-10 days post op.
In general, there would need to be a good reason to give vaccines at time of neutering that outweighed the potential downsides above.