My human baby is vaccinated. He is 2 months old. I think he got 2 vaccines already.
I have a tabby cat. She sometimes goes outside, but eats inside. I am not sure how clean she is. Not too dirty.
Can my human baby pet the cat? Is it okay to let the cat play with the human baby?
It's not easy to give one definitive answer - it's never really absolutely and completely safe, even healthy adults could get infected by pathogens transmitted from the cat. On the other hand - we humans, as species, don't derive our evolutionary success from obsessive avoidance of pathogens.
Also, a baby could potentially get infected in a wide variety of settings not involving this cat at all. For example a cat, especially outdoor one, could potentially transmit Salmonella - but a child could also happen to get infected with Salmonella while playing in a sandbox and putting fingers in the mouth, so it's wise not to become excessively focused on the cat in this context.
Depending on the source, one could find information that human immune system doesn't really mature until a few months of age, but also that it doesn't reach its full potential until adulthood. It isn't because either of these statements is wrong, it's just that the subject is extremely complicated and both of these statements are true in their respective contexts. I'd personally say it could generally be considered safe once the baby reaches a few months of age and isn't known to suffer from immune system disorders, but it's just my opinion and I'm not a medical professional as well.
As Trond Hansen suggested in the comment, having your baby vaccinated probably isn't really that important, because the vaccines of immunization schedule are targeted for diseases which are transmitted from human to human, and aren't known to be transmitted by cats (for example hepatitis B, as the hepatitis B virus (HBV) is only capable of infecting humans and higher primates), or do so only in extremely rare cases (for example tuberculosis).
Please also consider that the fact of your cat being outdoor increases the potential plethora of pathogens that it could transmit, and thus significantly increases the infection risk compared to what would be if the cat was to be indoor. Outdoor cats could prey on small animals, eat suspicious delicacies from garbage bins, etc. - all the related potential pathogens are then being methodically spread from mouth on the whole surface of cat's fur - seemingly and deceivingly clean fur - while it is grooming itself.
What is more, apart from the safety concerns related to pathogens - please take into account that all interactions between the baby and the cat need your constant supervision - not only for the baby's safety, but also for the cat's. And generally, all interactions between animals and children should be supervised if safety is to be the priority number one.
In conclusion, to get the most accurate and reliable answer I think it would be the best to just ask your child's pediatrician. They would have access to a lot of more specific data than we have there, and they would be able to examine and estimate the developmental level of your child's immune system in the context of this safety concern involving the cat.
You need to be present in the room if your child is to pet the cat. Young babies have little control of their body, so he might scare your cat. This might lead to the cat clawing or biting your child, so you need to stay close to him.
It is best to keep the cat away from your child when you are not present in the room and to keep the cat out of your child's bed during the night and during nap time. It is not as easy as it sounds to keep the cat away from a baby.
Be aware of a disease called cat scratch fever. I do not know how dangerous this is, but I think it is important for you to know about it.
There is two types of parasites your cat can transmit to your child. One is intestinal worms; you can reduce the risk for this by regular deworming of your cat.
The other type of parasite is Toxoplasma gondii which causes toxoplasmosis, and you can avoid your child getting infected by this by keeping your child away from the litterbox and away from the cat's poop.
Letting your child know the cat is a fine thing to do, but you need to be careful now in your child's first few months, do your best to make this a good experience for your child and for your cat.
For our 2 babies, the cat (>10 year old, ~8kg neutered tomcat) was moved to a relatives' home at the first months of the pregnancy and returned when the baby became heavier than the cat.
The weight was considered in order to discourage evenual cat's will to fight for a better position in the hierarchy (not that he tried, but one cannot constantly control neither the cat nor the kid).
Most cats keep themselves clean enough to be allowed in a human bed. Well, some of them don't, but we didn't have any problems.
Most cats are reluctant to stay with kids (or develop a healthy reluctance quickly) and prefer staying with the adults.
Be aware that the cat can develop parasites (both internal and external) even if never goes out. Consult your veterinarian about how to be sure your cat doesn't carry them.
edit: A friends of mine had young, but pretty cheeky cat that repeatedly got into the baby bed and slept with the baby when the baby was as young as 3-4 months (the cat was of a similar age).
Nothing bad happened.
