Only if they live in a sterile bubble. Otherwise, they can be exposed to potentially deadly diseases from very ordinary activities.
There are only two ways to develop immunity to an infectious disease. One is by getting the disease. That way is dangerous, as infectious diseases can cause significant and permanent disability or death. Tetanus, for example, is preventable by a vaccine every ten years. Without that vaccine, an incident as random and seemingly innocuous as having a rusty nail pierce your skin can cause you to get an incredibly painful illness that causes all of your muscles to contract and ends in death. And so on; I can go through symptoms and consequences of different vaccine-preventable diseases all day.
The other way to develop immunity is through vaccination, which exposes your immune system to portions of pathogenic organisms that cause it to develop an immune response. In this way, if you are exposed to a pathogen, your immune system immediately attacks and kills the pathogen without you ever being aware you were exposed.
Vaccines have saved countless millions of lives by preventing common diseases that used to kill most children before the age of five. One of the most horrific diseases known was wiped out due to vaccination. Infectious disease is no longer the top killer (still in the top ten, though).
As I said, vaccines are the most important and significant medical development ever.
BTW, if you have not guessed already, I am not susceptible to anti-vax propaganda. The same people who claim that there are too many people on earth and that the population should be reduced to some arbitrarily low number are the same ones trying to scare people with anti-vax hooey. You figure it out.
Not to thread hijack, but for what you say is DANGEROUS and blatently INCORRECT. Reader beware.