Full Series Needed for Full Immunity

Posted on Wed., May 05, 2010
By Dr. David Pepper

A patient's mother came to me puzzled. Why had her 3-month-old daughter been diagnosed with pertussis, after she had received the pertussis vaccine just a month before?

Pertussis is the P in the DTaP vaccine, given to infants in a series, at 2, 4 and 6 months of age. The disease is commonly known as whooping cough.

In children, whooping cough can be a severe respiratory infection, often requiring hospitalization. And in fact her infant daughter had been hospitalized for four days.

The reason this infant became ill despite having been vaccinated is that a first dose is just the start of becoming immune.

Usually all three shots in the series are needed for the best immunity and to prevent infection. Immunity often requires a series of shots, such as in the DTaP vaccines, and the Hepatitis B vaccine given in 3 shots over 6 months.

This is worth noting because recently the California Department of Public Health reported a rise in illness due to whooping cough. This is likely because some parents fear vaccines more than they fear the illness, so don't have their children vaccinated. Our past immunization campaigns have been so successful, that few have seen cases of diseases such as measles or pertussis, so don't realize how deadly they can be in children.

Getting immunized protects both our health and the health of those around us. This is what is meant when you hear the terms "community immunity" or "herd immunity."

Community immunity protects frail people, such as the very young, the very old and others who can't be vaccinated because of a medical condition.

For example, a child who has never had chicken pox or the chicken pox vaccine most likely will not become ill if everyone that child comes in contact with is immune to chicken pox.

Without community immunity, though, a few cases of disease could very easily—and very quickly—become hundreds of cases. This is how the 3-month old got whooping cough—someone in the community not immunized against whooping cough exposed her to it.

Through community immunity we have significantly reduced the spread of diseases like polio and small pox. While some parents may fear the minimal side effects (sore arm, slight fever) most of these parents have never seen or dealt with the real diseases, which can be devastating.

Vaccines work by imitating our bodies' own immune system.

When our bodies are infected with a germ (like a bacteria or virus), millions of our own white blood cells respond to fight off the unwelcome invader. When the battle is over and the body has recovered, cells known as memory cells hang around for years or longer and fight off the same germ if it seeks to infect us again.

Vaccines work in the same way, creating memory cells by exposing a person to a dead or weakened part of the germ (protein fragments in the vaccine), building immunity without causing illness.

May is National Toddler Immunization Month. Mark it by being sure your child's immunizations are up to date. Vaccinations protect your child and all of us.

Believe me, it's a lot better than getting the disease.

Find out more about childhood immunization at www.cchealth.org.

Dr. Pepper practices Family Medicine at the Martinez Health Center, part of Contra Costa Health Services, the county health department.