When Is a Baby Fully Protected by Vaccines?

Vaccines don’t confer 100 percent immunity, but when all children are immunized, it creates what is called herd immunity, which makes everyone safer, especially babies.



Q. I’m pro-vaccine and having a baby in a few months. My sister refused to vaccinate her two children, ages 1 and 5. How long will I need to keep them away from my baby in order to protect him or her from preventable diseases?

A. There’s no simple answer, because there are so many different diseases involved, and because the risk depends in large part on what is circulating in your community — which, in turn, may depend on how many of the parents in your community have your sister’s attitude.

Vaccines don’t confer 100 percent immunity, but when all children are immunized, it creates what is called herd immunity, which makes everyone safer, especially babies in those vulnerable early months of life. The way it works is that before babies are fully immunized themselves, they are protected by immunity in their caretakers, playmates and community.

Generally speaking, the younger the baby, the more dangerous some diseases can be.

Influenza, for example, can be severe in young babies, and we don’t start vaccinating till the child is 6 months old. A community with low immunization rates is a more dangerous place for small babies (and elderly adults and anyone with underlying medical problems) when flu season comes around.

Measles, mumps and chickenpox are all very much present in the United States, especially in underimmunized populations, and the vaccines for those diseases are usually not given until a baby is at least 12 months old (sometimes earlier if there’s an outbreak). Like flu, these are extremely contagious diseases, and measles in particular can be dangerous in small babies.

Starting at two months, your baby will be getting vaccinated against a whole range of diseases, some of them less likely to turn up in the United States (polio, diphtheria) and others far more common, like whooping cough (pertussis), again particularly dangerous in young infants, and also Streptococcus pneumonia and Haemophilus influenza Type B, which can cause pneumonia, meningitis and bacterial sepsis.

The early doses of vaccine do offer some protection, but it’s not complete. A child who stays on schedule will complete the basic series of immunizations by 15 to 18 months, but will still need a flu shot every fall to stay as protected as possible against influenza. More booster shots at 4 years old reinforce those childhood vaccines.

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