Natural infection with certain viruses can weaken the immune system. So when children are infected with one virus, they can’t fight off other viruses or bacteria as easily. 

This happens most notably during natural infection with chicken pox or measles. Children infected with chicken pox are susceptible to certain bacterial infections (MRSA or flesh-eating bacteria, for example). 

Children infected with measles are more susceptible to bacterial infections (resulting in sepsis) of the bloodstream. 

But vaccines are different.

It is true that natural infection almost always causes better immunity than vaccination. In fact, only the Hib and tetanus vaccines are better at inducing immunity than natural infection.

Natural infection causes immunity after just one infection, but vaccines usually create immunity only after several doses over a period of time.

The Myth - Infants are too young to get vaccinated.

The Truth - It’s very important to make sure that infants are fully immunized against certain diseases by the age of six months.