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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