A pregnant woman passes on antibodies to those diseases she herself is immune to. That may last for one month to one year, depending on a number of factors. And women cannot pass on immunity to all vaccinated diseases. So immunizations need to begin before natural immunity wears off.

The CDC recommends that this vaccine be given at birth and a second dose at age 1 to 2 months; please discuss with your child's health care provider to see whether a possible third dose is needed at age 6 months. This vaccine is especially important for infants who spend time in day-care centers or if the mother is hepatitis B positive, in which case the newborn is given both hepatitis B immune globulin and hepatitis B vaccine.

Hib vaccine prevents Haemophilus influenzae, type B infections, which can cause meningitis, pneumonia, and epiglottitis. The number of Hib meningitis cases have dropped dramatically since the vaccine was introduced. A meningococcal meningitis vaccine is also available, starting at age 11 or 12, to protect against another kind of meningitis.

A high fever, continual crying, or limp, listless behavior are signs of severe reaction that warrant a call to the doctor.

A mild illness, such as a cold with or without fever, shouldn't prevent immunization.

Today, the pertussis vaccine is acellular (the whole bacteria cell is not present) and is denoted as DTaP, a much safer form with minimal side effects.