A very important aspect of vaccination is the time between injection and development of protective immunity.
In most cases, with killed vaccines, two primary vaccinations are required to induce a sufficient level of protection and longevity of immunity. The first vaccine, the sensitizing dose, only primes the immune system and rarely induces adequate immunity by itself. A second vaccine, or booster, is required to increase an animal’s level of immunity to the satisfactory level. Most modified live vaccines, however, are able to stimulate the immune response after only one dose in an immunocompetent patient and in the absence of maternal antibodies.
An animal is expected to be immunized a week or two after the booster is administered. In other words, a vaccination program should be completed a week or two before exposure to the particular germ is expected.