What good does it do to have my pet vaccinated the same day as surgery? Surely they do not afford immediate protection.

You are correct, vaccines do not afford immediate protection. While protection is not immediate, neither is infection. It takes most viruses up to two weeks or longer for incubation time before an animal has clinical signs of infection. If that pet has never been vaccinated before, then it is a close race to protect the pet prior to the onset of disease, and, if the disease is not completely guarded against, then hopefully the illness will not be as severe because of vaccination.

Most pets have been vaccinated previous to this booster vaccination, in which case their immune response is much faster than if they were vaccinated for the first time.

The first time a pet is vaccinated, the immune system responds with a peak response in 3-4 weeks. On a graph, it would look like a bell curve. In puppies and kittens, we booster them every 3-4 weeks at the peak of their response. This allows the immune system to mount an even stronger response to later vaccines and exposure to viruses. At the end of the immune response, certain “memory cells” to that vaccine/virus are created. These memory cells stay in the body and they are responsible for protecting the pet if and when he is exposed to that virus. The better the vaccination process, the stronger the memory cells. When a pet is given booster vaccines or exposed to disease, the stimulation of the immune system occurs much more quickly because of the presence of the memory cells. The immune response is also stronger because the memory cells are strengthened and replenished.

So, for our pets that have been previously vaccinated, if they are vaccinated the same day as surgery, their immune response will be much quicker (peak response time is usually 5-7 days because of the memory cells) and will protect them from viruses that they may be exposed to that day or within the next few days. The immune system wins the race.

Of course, what is ideal is for the pet to be vaccinated 2-3 weeks prior to any potential stress or surgery that may suppress the immune system and make them more susceptible to disease.