To add to the ever-growing list of examples that highlight the necessity of vaccination, a new study published in Pediatrics has demonstrated that the source of the 2011 outbreak of measles in Minnesota was an unvaccinated child that contracted the infection whilst visiting Kenya.
The 30-month-old child was born in the US but was of Somali descent, living within a Somali immigrant community in Minneapolis which has low rates of vaccination. The child presented some symptoms of disease upon returning to the US from Kenya but unfortunately passed the infection on to a member of the same household and three children in a day-care center prior to diagnosis.
The disease then spread in several settings, resulting in over 3,000 individuals being exposed. Although only 21 cases were reported, it was the largest outbreak of measles in the area for over 20 years.
According to the study, 16 out of the 21 cases were not vaccinated, 9 of whom were age-eligible for the MMR. Of these 9 individuals, 7 were not vaccinated because of safety concerns.
Over the last decade there has been a significant drop the rates of MMR vaccine coverage among Somali children living in this community; in 2004 over 91% of children were vaccinated, in 2010 this fell to just 54%. This is likely due to the misinformation spread about the MMR vaccine. Although the original paper linking this vaccine to autism has been discredited, retracted and the author was found guilty of misconduct and fraud, it seems that some ideas are difficult to shed entirely. Luckily, an aggressive response by health officials and community leaders in the area halted this outbreak before it spread even further.
The authors of the study conclude that misunderstandings about vaccine safety must be effectively addressed in order to prevent further outbreaks which are avoidable.
Measles is a highly contagious disease and no vaccine is 100% effective. Furthermore, some people cannot get vaccinations for various reasons, such as being too young or having a compromised immune system. It’s therefore very easy for just one single case to cause an outbreak in a community. But if enough people are vaccinated, the vaccinated individuals will protect those without immunity (herd immunity) because disease transmission is interrupted. Drop below this critical number and an outbreak can easily occur, especially given the mobility of the human population and the fact that measles is still endemic in some countries.
It is also evident that many people believe that measles is not serious enough to warrant vaccination. It may therefore surprise some people to find out that, according to the CDC, 30% of cases develop one or more complications including pneumonia, ear infections or diarrhea. Around 1 in every 1,000 will develop an inflammation of the brain known as encephalitis which can lead to convulsions and may leave the child deaf or mentally retarded. Furthermore, 1 or 2 of every 1,000 children who contract measles will die.
These statistics are alarming given the fact that the US is currently experiencing a record number of measles cases; as of June 13 there have been 477 confirmed cases this year, the majority of whom were not vaccinated. This is the highest number of cases since measles elimination was declared in the US in 2000. Vaccination is important, don't listen to anecdote over peer reviewed evidence.
Image credit: CDC.