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Pixabay.com/Repeated vaccines (for parvovirus, canine distemper, feline viral rhinotracheitis, adenovirus, calicivirus and panleukopenia) are necessary to protect the health of kittens and puppies, but a lot of the owners misunderstand the reason behind it.The vaccine series (cases where the same vaccine is given multiple times) does not really boost the immunity of your kittenโs body after every single shot. In most of the cases, one or at the most two vaccines given in a space of four weeks is enough to produce full immunity as long as the body is able to respond to the vaccination. It is one of the major reasons why kittens and puppies need so many shots when they are still really young.Newborn animals usually have antibodies floating around in their circulatory system. They pick it up in utero or through the nursing colostrum from their mothers. The antibodies play a very important role in protecting kittens and puppies when their immune systems are still in development. This is a very good system because if the mother has come into contact with a particular pathogen, her child is likely to do the same.Maternal immunity directed against the vaccines received by the mom has an unintended consequence. It can end up inactivating the vaccines that are given to the offspring.The antibodies that the youngsters get from their mothers fade away in the first few months of their life, but the speed at which this happens tends to vary between individuals. There is no sure fire way of telling when exactly a kitten or puppyโs maternal immunity will wane, making him susceptible to disease and responsive to the vaccine.Research has shown that most of the kittens and puppies have a strong maternal immunity till they are eight weeks of age. This is one of the reasons veterinarians do not recommend administering the vaccination series before this point.Not only are most of the kittens and puppies adequately protected by their maternal immunity (assuming that their mothers are vaccinated), but vaccines that are administered before they are eight weeks of age are inactivated.Research has also demonstrated that maternal immunity wanes to the point where most of the youngsters are capable of responding to vaccination by the time they become 16 weeks old, which explains why they are given the last shots around this time.However, the two months between the eighth and the sixteenth week are highly problematical. Some youngsters who have a weak maternal immunity are highly susceptible to disease and start responding to vaccines any time between the eighth and the twelfth week. That is why vaccines are administered in 3 week intervals starting from the eighth week. It works as a good rule of thumb irrespective of when the petsโ natural maternal immunity fades.