Friday, January 27, 2017

Measles on The Oregon Trail and now

"John has measles." Our journey along The Oregon Trail wraps up with a member of our party falling ill with the measles virus. This leads to the stereotypical measles rash, along with fever and coughing. The mortality rate from measles tends to be low in developed countries, but in places of poverty and food shortages, the mortality rate can be as high as 28%. One of the biggest problems with measles is that it is highly contagious and can be spread through the air. There is also no treatment for this disease, leaving disease prevention as the best strategy for dealing with the measles.

While the march towards the eradication of measles has been well underway for many years, cases have begun to rise in number again recently. Just this week, an outbreak occurred in Los Angeles County, infecting 20 people so far. A vaccine for measles was developed in the 1960's, leading to a sharp decline in the number of cases in the U.S. almost immediately in the late 1960's. Global efforts to increase vaccination have been funded by the American Red Cross, the United Nations, the Centers for Disease Control, UNICEF, and the World Health Organization. The measles vaccine has also been improved over the years to provide better immunity to those vaccinated, giving us the MMR (measles-mumps-rubella) vaccine of today. Thanks to these efforts, measles deaths worldwide had decreased to just 164,000 in 2008.

Unfortunately, in 1998 a paper was written by Wakefield, et al. in The Lancet, showing a link between the MMR vaccine and autism. Although this paper was retracted by 10 of the 12 authors in 2004 and completely retracted by The Lancet in 2010, the publicity this paper received raised doubts for many parents about the safety of the vaccine for their children. Many people may still be unaware that in 2011, the authors of the paper were found guilty of deliberate fraud, which they had committed by picking and choosing what data to include in the paper. As a result, Andrew Wakefield, the lead author of the paper, had his United Kingdom medical license revoked. Even with the retraction and the slew of studies that followed, showing repeatedly no link between the vaccine and autism, parents have continued to voice concerns about vaccinating their children.

For a vaccine to eliminate disease, 100% vaccination is not essential. In vaccination there is a concept known as herd immunity, which has been defined as "the resistance to the spread of a contagious disease within a population that results if a sufficiently high proportion of individuals are immune to the disease." When a high percentage of the population is immune, the virus cannot be introduced or spread well because it will encounter too many hosts that are not susceptible to infection. For herd immunity to work for the measles, generally about 95% of the population needs to be vaccinated and immune. There have long been religious organizations that have opposed vaccination, as well as immunocompromised individuals who were not eligible for vaccination. Even with these small groups of people, high enough vaccination rates were reached to achieve herd immunity in many countries. Unfortunately, the recent increases in the number of parents actively choosing to not vaccinate their children due to fears of autism or other complications and the number of parents who simply do not see the benefit of vaccination and opt out has led to a decrease in the vaccination levels. This has made herd immunity much less effective, allowing cases of measles to increase again.

While the scientific community has repeatedly performed studies to test the safety of vaccines and found that there is no link between the MMR vaccine and autism, the negative publicity from the Wakefield, et al. paper has severely damaged the reputation of this vaccine. Re-educating the public about the safety and necessity of this, and other, vaccines has become a major priority in the wake of the number of measles outbreaks in Europe and the U.S. in recent years. With no treatment for measles, the MMR vaccine remains the only real hope for protecting the population from this highly contagious, yet preventable, disease.