Generally, we think of vaccines as protecting the vaccinated. We often forget that vaccines, when administered to enough people, protect those in the community who cannot be vaccinated due to certain health conditions, who are too young to be vaccinated, or who experience vaccine failure. This “herd immunity,” as it’s called, is analogous to the concept of ‘safety in numbers’ and is critical to outbreak prevention. However, as reported by Valerie Bauerlein and Betsy McKay in yesterday’s article “Where Could the Next Outbreak of Measles Be?” in The Wall Street Journal increasing numbers of vaccine exemptions in states such as California, Oregon, Washington, and Montana are threatening herd immunity. “Overall vaccination rates in some of these communities are under 80 percent, far below the threshold that is needed to prevent an outbreak for certain diseases.”
Approximately 95 percent of a community must be immunized against measles to ensure herd immunity, as the disease is highly contagious. According to the Centers for Disease Control and Prevention (CDC) , “measles is so contagious that if one person has it, 90 percent of the people close to that person who are not immune will also become infected with the measles virus.” The virus is spread through droplets and can remain in the air for up to 2 hours after an infected person has left the room. Complications from measles range from ear infections and pneumonia to miscarriage and death.
Due to the contagious nature of the disease and the increasing number of exemptions in which parents opt out of vaccination requirements for children, measles outbreaks have been a growing concern for public health officials. As has been recently reported by various news outlets, including USA Today, the 2012 Olympic Games in London this summer present a perfect opportunity for a large scale outbreak. In fact, most cases of measles in the U.S. are imported by unvaccinated American travelers returning home from abroad. A 2008 measles outbreak in San Diego was caused by an unvaccinated 7-year-old boy who contracted the disease in Switzerland and then passed it to children at his school and in his doctor’s office. To prevent such outbreaks, people in the community who are recommended to be vaccinated against measles and other diseases should receive these life-saving vaccines, if not to protect themselves to protect those who cannot get vaccinated.