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Childhood vaccination: protecting the herd

photo courtesy: James Cridland via flickr

Childhood vaccinations are a cornerstone of modern public health. Routine vaccinations have significant health benefits for the person being vaccinated – benefits that may be extended to someone who’s either not protected via vaccination or natural immunity. This protection is referred to as “herd immunity.”

Herd immunity is similar in principle to how a herd of elephants protects their babies. When a herd of elephants encounters danger, the adults form a ring around the babies, facing outward towards the danger. They become a barrier between the danger and the defenseless babies. But for the practice to work, there must be enough adult elephants to circle the baby elephants. If not, then the protection scheme is in danger of breaking down. The same thing happens with herd immunity.

For effective herd immunity to occur two conditions have to be achieved. First the vaccine must work very well and provide a long duration of protection to those that receive it (we see this type of protection in almost all routinely given childhood vaccines). Secondly there must be enough people protected via vaccination or natural immunity around the individual(s) not protected to limit the spread of an infectious disease. When both of these conditions occur an infectious disease is not able to spread to those not protected because there are so many people protected in the group. This concept is visualized (link to visualized http://www.niaid.nih.gov/topics/pages/communityimmunity.aspx) by the National Institute of Allergy and Infectious Disease.

Today herd immunity is not always guaranteed. Some individuals refuse vaccination and may routinely associate with others that also refuse vaccination. If a vaccine preventable infectious disease is introduced to a group such as this, then it’s likely an outbreak will occur as there is simply not enough protected individuals in that group. Individuals that are not protected (either by vaccination or other medical reasons) also interact frequently with the rest of the community which can create small groups of individuals that are susceptible to vaccine preventable infectious disease. Some vaccines, like the whooping cough vaccine, provide high levels of protection but do not have the duration of protection desired. This allows for outbreaks to occur in highly vaccinated groups.

Just like with a herd of elephants, the more protection you have the better off you typically are. Sticking to that childhood vaccine schedule will help ensure that your child protected.  And they may just help defend against illness in others.

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