There are millions a viruses and bacteria that could all potentially be deadly. Just because we vaccinate for a hand full of them does not really prevent much. And the ones we do have vaccines for may even be beneficial for the child's immune system development.
Tell your brother immunology is a research field not a proven science and vaccines are nothing more than an experiment. No immunologist can tell you what exactly happens to the vaccine once it is injected into your body. Now can they tell which child will suffer a severe reaction.
Each human body is its own ecosystem and to treat each and every child the same is rediculous. We have not idea what this child's constitution needs to develop properly and get a strong immune system to fight of cancer and much worse diseases.
We are basically trading normal childhood diseases for childhood cancers, autism, ADHD, MS, juv. diabetes, juv. rheumatism, allergies and asthma etc, etc,
In 100 yrs from now they will most likely wonder how we ever let that happen to our kids.
We don't ever worry about a hand full of infections that my dh and I had when we were kids.