A pregnant woman passes on antibodies to those diseases she herself is immune to. This natural immunity lasts for a very short time. 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.

About 1 in 4 children will have swelling or tenderness at the injection site or a low-grade fever. High fever, continual crying, or limp, listless behavior is rare. Any of these is a sign of severe reaction that warrants a call to the doctor.

An infant should not get this vaccine if the child had a serious allergic reaction or encephalopathy after a vaccine given earlier. 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.