Vaccination protects your pet against several highly infectious and sometimes fatal diseases. Vaccination is especially important for young animals, not only because their immune systems are not fully developed but also so they can be socialized to new experiences and other animals safely.
Young animals get most of their immunity from their mother's milk. Once weaned, they stop receiving this immunity and will need to develop their own. A vaccination stimulates their bodies to produce immunity against these diseases but it still takes some time after vaccination for young animals to produce these antibodies on their own.
If not kept in a clean, stress-free environment during this time, young puppies and kittens can still fall sick despite vaccination. The SPCA sees many pet shop animals that still fall sick despite vaccination because they are kept in poor conditions and do not manage to build up sufficient immunity against the disease or may have been born to unvaccinated mothers.
Ensure that your puppy or kitten was born to a vaccinated mother, has been fully weaned for several weeks and that it was born and raised in a clean, stress-free environment.
In Hong Kong, it is against the law to sell unvaccinated, unweaned animals.