How do some children of the country develop immune to Hapetitis A at 5 years age itself - Science - Why Do We Fall Ill

Question

How do some children of the country develop immune to Hapetitis
A at 5 years age itself?

Mushtaq Ahmed · Accepted Answer

Children get immune to Hepatitis A by the age of 5 years by
itself if they are exposed to the infection previously Our immune
system has the ability to remember the virus and when the same
virus attacks the child next time 
disease will
not be manifested
Moreover immunity to hepatitis A is also conferred due to
vaccination Till the age of 5 children are given regular vaccines
which make them immune to many diseases like Hepatitis A

How do some children of the country develop immune to Hapetitis A at 5 years age itself?