Answer
The infant will develop artificially acquired active immunity.
Work Step by Step
The vaccines contains a weakened form of the virus, since the virus is weakened it does not cause much harm to the body and the primary immune system fights off the virus in few days and due to this the memory B cells and T cells are created which store the information about the antigens carried by the virus so if the virus attacks again the memory cells can provide the information to fight the disease. This is called artificially acquired active immunity.
