Monday, May 6, 2019

Tinder for Measles Outbreaks

Environmental & Science Education
Edward Hessler

More than 700 cases of measles have been reported this year according to the Center for Disease Control (CDC). Helen Branswell, writing for STAT, notes that "With the year only a third of the way through and measles spreading in a number of outbreaks across the country, this year's total could well top the 1994's 963 cases."

We are not alone in this struggle with measles. It is international. Branswell continues "More than 112,000 measles cases were recorded globally in the first three months of the year, with major epidemics in countries including Ukraine, Israel, and the Philippines.

Branswell's report is mostly about the growing number of people susceptible to measles, tinder for future outbreaks as she puts it. In a recent United Nations survey of 10 high-income countries, "the United States topped the list of nations in terms of percentage of children who were not vaccinated against measles from 2010 to 2017, with an estimated 2.6 million children who didn't receive their first dose of measles vaccine during that period.

As you know the measles vaccine is effective, protecting some 97 percent of those vaccinated from the disease. Measles vaccination is a two-step affair with the first vaccination occurring around the time of a child's first birthday and the second, between the ages of four and six years old.

You may wonder about the 3 percent who think they are protected. They are susceptible but what protects them is "herd immunity, the phenomenon where enough people in a population are immune to the pathogen that it cannot effectively spread within it."  This is what we depend on but now we are threatening such immunity. "Nationally," according to Branswell, "the percentage of children who received one or more doses of measles-containing vaccine remained pretty stable between 2013 and 2017, hovering between 91.1% and 91.9%." However, this is "near the lower end of the vaccination rates--between 90% and 95%--needed to maintain herd immunity...."

There is another problem with measles and that is the distribution of those susceptible which is not even across the U.S.. There are pockets or clusters e.g., "Brooklyn and in Rockland Country, north of Manhattan, where transmission is largely occurring among unvaccinated familes of Orthodox Jews. ... And "California, for instance has seen low vaccination rates among children in some affluent, highly educated families...." 

Branswell cites Dr. Karen Smith, director of the California Department of Public Health who notes, "'Overwhelmingly the schools that have very low vaccination rates tend to be the Waldorf schools, the Montessori schools, but also then a number of charter schools. Most of those are small schools that cater to a very specific community.'"

And there are other factors, e.g., the role of  probability, increased today by international travel where a susceptible travelercan return infected and not know it but able to start an outbreak(s) elsewhere. This probability is made more likely when the level of protection among the general population is lowered. Another factor is states and counties that have non-medical exemptions.

Branswell's essay contains an animated video on what makes measles so contagious and, of course, more details.

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