- Aim is to provide active, vaccine-derived immunity as early as possible.
- But maternally derived antibody (MDA) may block effective vaccination in young animals. As MDA declines, they may become susceptible to infection before they are responsive to vaccination, leaving an immunity gap ( Figure 1 ). Some vaccines are better at overcoming MDA than others.
- In most diseases MDA declines to non-interfering levels in the majority of cats and dogs by 9-12 weeks of age. The standard protocol is often therefore to vaccinate at 8 or 9 weeks and then repeat at 12 weeks old.
- Where puppies and kittens can be kept isolated and the risk of infection is low, one vaccine dose at 12 weeks of age will often suffice, particularly for modified live vaccines.
- Extra doses of vaccine earlier and/or later than standard may be given. For example, earlier doses may be given during an outbreak of disease or when puppies or kittens are deprived of colostrum and are known to be at risk. Later doses might be appropriate if the mother is likely to pass on high levels of MDA, for example if there was a history of clinical disease.
- Figure 1 shows the decline in serum levels of maternally derived antibody (MDA) in puppies and kittens. Approximately 80-98% MDA in puppies and kittens is derived from colostrum, that is from milk absorbed during the first 24 hours after birth. The graph demonstrates the decline in antibody titre (half-life approximated at 10 days) over the first 100 days of life, and the dotted lines indicate how variation in initial titre between and within litters can affect how long MDA persists. This shows how vaccines given too early will be blocked by MDA, and that, because attenuated vaccine viruses are less virulent than wild-type viruses, there will almost always be a short period (the immunity gap) when effective vaccination is impossible but the animal is susceptible to wild-type infection and disease. Furthermore, through variation in antibody titre in queens and bitches and in colostrum uptake by puppies and kittens, the optimum vaccination time will differ between individuals.
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