Vaccinations and Herd Immunity

We are once again finding ourselves in the middle of a measles outbreak in the United States. And once again, vaccinations are the topic of a national debate.

In 2014, the United States experienced the largest measles outbreak since it was considered eliminated in 2000. The 2014 outbreak included 23 separate outbreaks with a total of 644 cases in 27 states. In this context, “eliminated” means there isn’t a constant presence of the disease in an area not that it no longer exists. That being said, there is always a risk that measles could reestablish itself within the United States. This risk can become a reality when large portions of a population are not vaccinated against the disease.

According to the latest update from the CDC, this most recent outbreak of measles has reached 18 jurisdictions and there were 125 confirmed cases. A large numbers of the cases are part of an outbreak that began at Disneyland in Southern California. Public health officials suspect that the outbreak was a result of an infected person from outside the United States who visited the theme park. The disease was able to take hold because of the high rate of individuals who were unvaccinated.

Although it is recommended that parents have their children vaccinated, it is not required. Parents can opt out of having their child vaccinated for religious or personal reasons. Medical reasons such as an anaphylactic allergic response to the vaccine prevent some people from being able to receive a vaccination.

So how to vaccines protect us? Vaccines can save lives by preventing outbreaks of diseases. In order for vaccinations to work, a large portion of a community needs to receive the vaccination to provide protection against an outbreak of a disease. When a large portion of a community is vaccinated it protects those individuals in a community who are unable to receive a vaccination such as infants, pregnant women, and immunocompromised individuals.

When a large portion of the community is immunized it is known as herd immunity or community immunity. Herd immunity is defined as “the resistance to the spread of infectious disease in a group because susceptible members are few, making transmission from an infected member unlikely.” When an infected individual enters a community, herd immunity will break the chain of infection, making it difficult for a disease to spread. The following graphic from the National Institute of Allergy and Infectious Disease (NIAID) provides a great visual that explains how herd immunity works.


This current measles outbreak once again provides health communicators with a unique opportunity. We are able to use this opportunity to educate those around us about the importance of a receiving vaccinations and the positive impact it has on the community.

Original post.


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