In the United States, the Centre of Disease Control reports that there have been 159 cases of measles from January to August 2013, including 8 domestic outbreaks accounting for 77% of all cases.
The CDC characterizes an outbreak as a transmission chain with three or more confirmed case. The largest outbreak in 2013 to date involved 58 cases of measles in New York City. During 2001 to 2012, there were a median of 60 measles cases in the US, with a median of two outbreaks.
The interesting thing here is that measles was declared to be eliminated in the US in 2000, though 20 million cases occur every year in the rest of the world, including a 2011 Quebec outbreak of 725 cases. As a result, American health professionals are no longer trained to identify and treat measles.
Measles (also known as rubeola) is a viral illness characterized by fever, cough, runny nose, red eyes, and most distinctively, a body rash. It is spread through respiration and highly contagious: this leads to distinct, localized outbreaks of infection in a largely vaccinated population. It rarely causes death but can result in deafness and pneumonia.
82% of those who contracted measles in the US this year so far were unvaccinated, and 9% were unsure of their vaccination status. Persons who can’t or won’t get vaccinated due to medical or philosophical reasons rely on herd immunity to protect themselves: if none of their peers can get ill, then they won’t either. Herd immunity is a form of collective immunity of a population, developed when a large enough proportion of the population is resistant to the disease to prevent the disease from forming long chains of transmission. The percentage of individuals that must be resistant to the disease to prevent its spread through a well-mixed population is dependent on the basic reproduction number (R0) of the disease, through the relationship %Vaccinated=1-1/R0.
R0 is a parameter that represents the number of individuals an infectious organism can start during its lifetime. R0 depends on factors like the longevity of the organism, and type of transmission. Measles is infectious for four to nine days, and is airborne, thus has an R0 of 12 to 18. Consequently, 92 to 94% of a population must be vaccinated against measles for outbreaks to be prevented.
However, in the United States, the vaccination rate among young children is only 91%. The vaccination rate for measles in Canada is 85%. The vaccination rate for measles in Britain, the birthplace of the anti-vaccination movement, fell from a peak of 92% to 73% today.
The modern anti-vaccination movement began in the late 1990s, when British physician Andrew Wakefield warned that measles, mumps, and rubella vaccines caused autism in children. His claims have since been refuted but the fear remains. Activists such as Jenny McCarthy and Robert F Kennedy Jr. still campaign against vaccinations for children. Today, 80% of unimmunized individuals refused the vaccine for philosophical objections.
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