Читать книгу The Power of Plagues - Irwin W. Sherman - Страница 15

In the year 2015, for some, Disneyland wasn’t the happiest place on Earth. It was in January of that year that a single measles-infected individual was able to spread the disease to 145 people in the United States and a dozen others in Canada and Mexico. Patient zero in the 3-month-old Disneyland outbreak was probably exposed to measles overseas and while contagious unknowingly visited the park. (The measles strain in the Disneyland outbreak was found to be identical to one that spread through the Philippines in 2014, where it sickened ~50,000 and killed 110. It is likely that patient zero acquired the virus there.)

Measles spreads from person to person by sneezing and coughing; the virus particles are hardy and can survive as long as 2 h on doorknobs, handrails, elevator buttons, and even in air. For the first 10 to 14 days after infection, there are no signs or symptoms. A mild to moderate fever, often accompanied by a persistent cough, runny nose, inflamed eyes (conjunctivitis), and sore throat, follows. This relatively mild illness may last 2 or 3 days. Over the next few days, the rash spreads down the arms and trunk, then over the thighs, lower legs, and feet. At the same time, fever rises sharply, often as high as 104 to 105.8ºF (40 to 41ºC). The rash gradually recedes, and usually lifelong immunity follows recovery. Complications, which may include diarrhea, blindness, inflammation of the brain, and pneumonia, occur in ~30% of cases. Between 1912 and 1916 there were 5,300 measles deaths per year in the United States. Yet all that changed in 1968 with the introduction of the measles vaccine; in the United States, measles was declared eliminated in 2000.

What, then, underlies the Disneyland outbreak?

On average, every measles-infected person is able to spread the disease to ten other people, i.e., its R₀ value is 10. With this multiplier, measles will spread explosively; indeed, with multiplication every 2 weeks and without any effective control (such as immunization), millions could become infected in a few months. It has been estimated that to eliminate measles (and whooping cough) ~95% of children under the age of 2 must be immunized. For disease elimination not everyone in the population need be immunized, but it is necessary to reduce the number of susceptible individuals below a critical point (called herd immunity).

An analysis of the Disneyland outbreak of measles shows that that those infected were unvaccinated. The researchers have calculated that the number of vaccinated individuals might have been as low as 50%. The outbreak that began in California was a reflection of the anti-vaccination movement, which had led some parents to believe the false claim that the vaccine for measles caused an increase in autism. (The “evidence” for this was based on just 12 children and has been thoroughly discredited by massive studies involving half a million children in Denmark and 2 million children in Sweden.) Then, too, some parents believe their children are being immunized too often and with too much vaccine because pharmaceutical companies are recklessly promoting vaccination in pursuit of profit. Other parents contend that the vaccine is in itself dangerous. It is not, as is evidenced in Orange County, where Disneyland is located: the outbreak sickened 35 people, including 14 children. And although a measles vaccine has been available worldwide for decades, according to the WHO, about 400 people a day died in 2013.

The response to the outbreak at Disneyland prompted the California Senate to pass a bill, SB 277, which required almost all California schoolchildren to be fully vaccinated in order to attend public or private school, regardless of their parents’ personal or religious beliefs. In signing the bill, Governor Edmund G. (Jerry) Brown wrote: “While it is true that no medical intervention is without risk, the evidence shows that immunization powerfully benefits and protects the community.”