The first vaccination

A course of two or three vaccinations is usually given as a primary course. This is because the maternal immunity falls at different times in different puppies and so they become susceptible to disease at different times. Also, the Leptospirosis part of the vaccine requires the immune system to be 'primed' by the first dose of vaccine so that the second dose can produce full protective levels of immunity.

Vaccines work by stimulating the body to produce its own defence against infection. One of the key components of this "defence" is antibody and as we saw in the previous section, this natural defence or protection can be passed temporarily ("passively") from mother to offspring (MDA).

Whilst there is a high enough level of MDA to protect the young puppy or kitten, MDA can actually interfere with successful vaccination. This is because, although a vaccine is a modified harmless form of the disease, it is "seen" by MDA as an invader. MDA therefore assumes its protective role and neutralises the vaccine.

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