Parvo is kickin my butt

The reason you give pups multiple injections of the same vaccintaion has nothing to do with how long the vaccination lasts, how strong it is, or anything of the sort.

Without a bunch of scientific BS, pups receive one dose of antibodies from their mother. It is delivered in the "fore-milk" which is colostrum they drink the first day or two they are born. Colostrum contains a transfer factor that allows the antibodies to be absorbed and not killed and digested like anything that would normally be injested.

The mothers antibodies which are passed last for a non-specific time, but will render any given vaccination useless as long as they are in the pups system. By giving multiple injections, the attempt is to try and hit what is called the "window of susceptibility" when the vaccination will not be killed, and will become effective. Injections given past that point are worthless, however there is no way to know when that period is because it varies.

This is why some pups who have been properly vaccinated can and do sometimes catch the virus...due to the fact by a stroke of bad luck perhaps they were vaccinated either too early or to late having been exposed to the virus during that window period.

Another thing worthy of mentioning is the importance of the mother having been properly vaccinated. If she had not, the pups won't receive near the amount of antibodies they otherwise should have and it can greatly increase their chances of becoming infected.