Kittens can be vaccinated starting with 8 weeks old. Is the age when they can receive the first polyvalent vaccine. 3 weeks later the kitten will receive again the same vaccine. Some vets make even a third vaccine to the kittens.
This kitten for example is over 9 weeks old already ad he and his brothers received already the first vaccine. Is very very important to let your kittens be vaccinated because the vaccine will protect them against at leat 3 diseases that can easily kill your kitten.
I tell you from my experience, I have seen what can happen to kittens that are not vaccinated when they get ill and is terrible. Some of them even die. All the kittens that I rescue get their vaccines done and it never happened for a vaccinated kitten to get ill with the diseases that the vaccine covers, never. Even if a vaccinated kitten had contact by accident with an ill kitten, the vaccinated kitten never took the disease. And I am doing this since over 14 years.
Is also very important when you have a small kitten that is not vaccinated to keep the kitten in a clean place, better in the same room until he gets fully vaccinated or at least for 10 days after the first vaccine and never enter in the room where the kitten is with the same shoes that you use to go outside. Also never let the kitten have access at the shoes that you use to go outside. Some diseases can be brought to the kittens even by us on our shoes or on our clothes.
So vaccinating your kitten is truly important and just by taking some simple measures you can save your kittens life.