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 and to protect a baby from all vaccine-preventable illnesses.

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.