The immunity a baby receives from his mother lasts only about three months?

Yes: The infant gradually begins to form his/her active immunity program. That is why, in my view, it is wrong to give any form of vaccination on day one and the reason that immunization vaccines are delayed until the physiology of the infant has matured.

In most cases: Premi infants tend to get less transfer and this fades quicker. If the mother never developed antibodies to an illness like Hepatitis B, her antibodies would not block the effectiveness of a newborn Hep B shot, but might prevent the common baby shots from having a benefit. That is why we start at 6-8 wks for many of them.