Experts say the trend is worrying given dogs and cats spend more time outdoors, and around potential spreading agents like mud and faeces.
The People's Dispensary for Sick Animals (PDSA) charity say a quarter of dog owners now say their pet hasn't had any vaccines when they're puppies - equating to 2.2 million dogs being left open to horrible diseases.
Animal welfare charity Blue Cross says two of the vaccines commonly skipped - parvovirus, a virus that attacks cells in a dog's intestines, and distemper, which is basically canine to measles - can both be fatal to dogs.
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