Wednesday, December 14, 2016

Anti-Vaccers: A threat to Disease Extinction

Across America, parents are making the damning decision to not vaccinate their children. Upon exploring a vaccine resistance blog, claims for vaccine scandals, government propaganda, secret pathogen exposure, and causative mechanisms for Autism appear to push people away from the idea of getting vaccinated.[1] But what exactly is this movement doing for the prevalence of virulent diseases in the American population? According to the Council on Foreign Relations’ interactive map, America has been experience clusters, outbreaks, and epidemics of vaccine-preventable diseases since 2008.[2]  Preventable diseases include: whooping cough, mumps, and measles. In 2015, Texas experienced a widespread outbreak of measles as the disease’s vaccination fell dangerously close to the percentage needed to enact herd immunity (95%).[3] The Texas Department of State Health Services reported over 45,000 children not complying with school immunization laws because of non-medical reasons, a.k.a. personal opinions. 3 This is double the number of exemptions from 2010 and 19 times greater than in 2003, accompanying a growing anti-vaccination movement (Figure 1, Figure 2). 3,[4] The CDC and VeryWell (a user friendly health information site run by About, Inc.) demonstrate the excessive number of outbreaks that have occurred over the past 5 years.[5], [6]

With the growing number of vaccine exemptions, an epidemiological study was conducted to estimate the number of measles-susceptible children and adolescents present in the United States. Typically, vaccination rates are high enough to induce immunity among the population. For measles virus, MMR vaccine coverage needs to be relatively high (92-95%) in order to prevent clusters and outbreaks of infection because the R0 is 12-18. 3 This study is the first to aggressively quantify the number of susceptible in children and adolescents in the US and how this relates to the herd immunity threshold.[7] Efforts to report the number of people susceptible to measles are predicted to aid in planning for measles outbreaks and emphasize the need for maintaining immunization coverage.

Berdnarczyk and colleagues retrieved data from the National Immunization Survey-Teen (NIS-Teen) available through the CDC.[8] Data from 2008-2013was normalized and analyzed the age at which individuals were vaccinated and the effectiveness of the MMR vaccine.8 They also took into account transplacental transfer of measles antibodies and adolescent cancer treatment. In the sensitivity analysis, variation estimates were calculated for vaccine coverage, vaccine effectiveness and duration of maternal antibody protection, leading to a 0.98 multiplier for age-specific vaccine coverage estimates to take into account decreases in immunization coverage.8 Their results were compared to the herd immunity threshold of 92% to provide a point of reference for future studies. All analysis was based on 18 cumulative birth cohorts consisting of 69,856,092 children and adolescents reported in the NIS-Teen. 8

As a result of data analysis, Berdnarczyk and colleagues estimated 8,714,275 (12.5%) of the population in question to be susceptible to measles.8 24.7% of children aged 3 years or younger were found to be not immune while 9% of children and adolescents aged 4-17 years were susceptible. Shockingly, the oldest population (13-17 years old) had over 1.5 million individuals not immune to measles even though they had the longest amount of time to get vaccinated.8  Results appear to demonstrate that overall, children and adolescents under the age of 17 are not reaching the heard immunity threshold (87.5% of the population is immune) but within individual age groups, except for children under three, the herd immunity threshold is roughly met. Sensitivity adjustments determined 13.4% of children under the age of 17 were susceptible to the disease with the variation estimates potentially throwing some age groups under the desired threshold for immunity. 8  Maternal antibody protection through placental transfer before birth brings this number down to 10.6% of the population being susceptible. Figure 3 highlights the geographic regions where susceptible children and adolescents are residing, acknowledging trends of vaccine exemptions and areas for potential measles outbreaks (Figure 3). 8 Ultimately, the study concluded that although immunity levels are within the herd immunity threshold, there are risks for these levels to drop and certain age groups are more at risk than others.

This study utilized crude survey data to attempt an estimation of all susceptible children and adolescents in America. Although, based on the nature of the study, it is difficult to accept the results as fact, it raises a terrifying point that approximately 10-13% of the American youth aren’t immune to measles. Measles is a highly contagious virus that can quickly cause outbreaks in confined areas such as schools, playgrounds and even Disneyland. It disproportionately affects youth populations, who already have poor hygiene skills and interact in close proximity to each other, making the disease even more important to vaccinate against. Vaccine resistance movements threaten herd immunity thresholds and lead to outbreaks of measles, as observed in Texas in 2015. 3,4  It is important to recognize that members of these movements aren’t “dumb” but are rather having difficulty interpreting scientific data and conquering their initial impressions and paranoia surrounding vaccines. Communication about the benefits of vaccines and that several studies have debunked the theory that the MMR vaccine causes autism needs to be established with the movement for the benefit of the general public.[9] I believe that every one is entitled to uphold their own beliefs, and in America, we as a people are able to make our own decisions concerning health care. However, when evidence indicates that a virus has potential to be eradicated or there is a preventive measure to ensure my loved ones and myself won’t experience a serious disease, it stands in the best interest that the vaccine is mandated for the population as long as no serious side effects are observed. The anti-vaccination movement is affecting how health-care workers are able to do their jobs and the way public health policy is shaped. For now, schools are extending non-medical exceptions for vaccinations, but only time will tell how the movement will affect public health policy for the country.

[1] Vaccine Resistance Movement website: http://vaccineresistancemovement.org/ The website highlights main reasons to avoid vaccines and other alternatives.
[2] Council on Foreign Relations interactive Global Map of Vaccine-Preventable Outbreaks. http://www.cfr.org/interactives/GH_Vaccine_Map/#map . The map addresses all the possible outbreaks of serious illnesses that could have been avoided if the affected populations were vaccinated.
[3] Hotez, Peter J. (2016) Texas and Its Measles Epidemics. PLoS Med. 13. 10.
[4] A policy brief by Rice University’s Baker Institute for Public Policy that performs a case study on Texas School-Entry Vaccinations. I highly recommend reading this report as a compliment to this blog post. It can be found here: https://scholarship.rice.edu/bitstream/handle/1911/92690/BI-Brief-101316-STP_Vaccines.pdf?sequence=1&isAllowed=y
[5] The CDC’s breakdown of the outbreaks of Measles across the United States: https://www.cdc.gov/measles/cases-outbreaks.html
[6] VeryWell provides easy to understand health information, tips and advice to the general public. The site outlines all the outbreaks of Measles in 2015, including Texas and Disneyland. https://www.verywell.com/measles-outbreaks-2633845
[7] Bednarczyk, R. A., Orenstein, W. A. & Omer, S. B. (2016) Estimating the Number of Measles-Susceptible Children and Adolescents in the United Staes Using data From the National Immunization Survey-Teen (NIS-Teen). American Journal of Epidemiology. 184. 2.148-156.  
[8] The CDC conducts the NIS-Teen to estimate US vaccine coverage. Data is located on the CDC website: https://www.cdc.gov/vaccines/imz-managers/coverage/nis/teen/index.html
[9] Dales, L., Hammer, S. J. & Smith, N. J. (2001) Time trends in Autism and in MMR Immunization Coverage in California. Journal of the American Medical Association. 285. 9. 1183-1185.

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