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.

Current Hand, Foot & Mouth Disease Outbreaks. How Can We Study It?

Recently, news headlines have stirred panic among the American public depicting a “highly contagious viral infection” as a threat to not only children, but now adults as well. Localized infections of Hand, Foot and Mouth Disease (HFMD) arose on university campuses in Illinois and Florida this past summer and the virus has been sporadically in the news since then. Symptoms of the common infection caused by Coxsackievirus A16 include fever, sore throat, painful sores around and inside the mouth that could become ulcers and a skin rash with red spots that could develop into blisters on the surface of hands and feet, knees, elbows, buttocks or genitalia.[1],[2],[10] Although the disease is usually benign, Coxsackievirus A16, though more commonly Enterovirus 71, pathogenesis has potential to induce fatalities. Coxsackievirus A16 caused the death of a 15-month-old boy in 2005 and a 2000 Enterovirus A71 outbreak in Singapore resulted in several deaths.[3], [4] Enterovirus A71 virus targets epithelial cells and the walls of the gastrointestinal tract, but secondary infections occasionally attack the nervous system leading to more severe consequences.[5] Persistent infections, although rare, can cause a variety of complications, including aspetic meningitis, brain-stem encephalitis, poliomyelitis-like paralysis, pleurodynia, myocarditis, and death.[5] 

For a fairly common disease among children, little is known about how to prevent Enterovirus A71 infection. In a paper released earlier this year, Win Kyaw Phyu and colleagues progressed a small animal model to study the disease, highlighting a potential vaccine development against the more virulent HFMD.[6] The non-enveloped, single-stranded, (+)-RNA virus is transmitted through fecal-oral and oral-oral routes, most commonly in pediatric populations, though current outbreaks are affect young adult and adult populations. Enterovirus A71 probably reaches neurons through viremia, establishing an infection that can cause encephalomyelitis.[7] Previous studies have used a mouse model to describe retrograde axonal viral transport from peripheral nerves to infect neurons in the central nervous system (CNS), but these models were based on direct inoculum injected into the spinal cord or muscle tissue instead of the natural route of transmission.[8] Here, Phyu and colleagues further establish a hamster model as suitable for Enterovirus A71 infection through oral infection and highlights potential protective qualities of a mouse-adapted virus.[6][9]

The experiment was performed on 2-week-old Syrian golden hamsters, which demonstrated consistent infection by oral-route, with an Enterovirus A71 mouse-adapted virus (EV-A71 MAV) at a 50% lethal dose (LD50) calculated using the method of Reed & Muench (25 CCID50).[6] 6 groups of 6 hamsters were orally infected with PBS containing 105, 104, 103, 102, 10, and 1 CCID50 of inoculum, examining every 3 hours for 14 days for signs of infections including weight loss, humped posture, ruffled fur and hind limb paralysis.[6] 17 animals were found with limb paralysis and were euthanized. 7 had died overnight and were excluded in analysis of tissue samples. After 14 days, the skin was separated from the carcasses and cross-sections of the oral-cavity, brain, spinal cord, internal organs, limb muscles and paws were taken for analysis. A second experiment infected 8, 2-week-old hamsters with 104 CCID50 for correlation with pathological findings by analyzing serum and solid organs in addition to skin and cross-sections.[6]Tissue sections were stained with hematoxylin and eosin for light microscopy and then additionally prepared for immunohistochemistry (IHC) and in situ hybridization (ISH).

Results from the LD50 experiment determined survival of the hamsters was dose-dependent with complete fatality of all animals infected with 102 CCID50 or higher between 3 to 8 days post infection, displaying clear signs of the disease (Figure 1).[6] These animals also showed macroscopic skin ulcers/leisons around the nose, lip and paw. 16.7% of animals died in the low 10 CCID50 group with all surviving animals not displaying any signs of illness and only one animal in the 1 CCID50 group developed limb paralysis on the 10th day after infection, recovering 4 days afterwards.[6] In all animals, IHC and ISH displayed strong positive signals indicating small foci of viral antigens/RNA in the epithelium covering parts of the oral cavity, paws, limbs, head, neck, chest, and even the hair follicle germline. Most importantly, the oral infection stimulated viral replication in neuronal bodies in the brainstem (62% of animals), spinal cord anterior horn (90% of animals) and in sensory ganglia (90% of animals) as depicted by the presence of viral antigens and RNA via IHC and ISH positive signals (Figure 2).[6]  
Phyu and colleagues further expanded on previous knowledge of EV-A71 by inducing an epithelial and neuronal infection in hamsters via oral routes.  Identifying viral particles in oral cavities and skin lesions confirms the transmission of the virus and how person-to-person contact is likely to generate outbreaks, like the one currently being observed in the US. The study also determined the absence of viral particles in the gastrointestinal tract signifying that viral replication in these areas are insufficient to cause transmission of the virus and consistent with human oral tests for the virus are more likely to be positive than rectal swabs.[6] Phyu and colleagues also suggest that EV-A71 presence in that retrograde axonal transport of the virus to CNS neurons through viremia is important in pathogenesis, consistent with previous studies.[6],[8] This hamster model was also found to be more susceptible to infection of EV-A71 after oral infection of MAV.[6]Other mice models have not established a consistent infection of EV-A71, but inoculum with EV-A71 and MAV establishes a persistent infection of HFMD for study.[6]Researchers involved hypothesize that the susceptibility stems from immune system immaturity and availability of viral receptors.[6]  

The importance of this model revolves around the benign nature of HFMD. HFMD doesn’t cause severe complications unless the infection becomes persistent. Establishment of a consistent disease in a small animal model allows researchers to analyze viral pathogenesis, assess why the virus has preference for neurons upon secondary infection, and how the virus is able to do this. Insight into viral mechanisms generates new ways to attack the virus with anti viral drugs and even a vaccine. Although this study outlined and confirmed previous knowledge, I do not believe they did enough original work. Perhaps they should have further isolated the virus in neuronal tissues, such as the spinal cord and brain stem, to isolate viral proteins and attempted a subunit vaccine. The researchers successfully established that the virus was dose dependent and produced a persistent infection in the presence of MAV, but this model had already been done before. If they had attempted to inoculate some hamsters at birth with some of EV-A71’s proteins in a third experiment, they would have not only confirmed that the hamster model using MAV was an efficient way to study the virus, but also an effective way to derive and test vaccines. As someone who works in a child-care facility, I know all too well that once one toddler has HFMD, the entire center will start breaking out in tiny blisters. It is a painful disease for pediatric victims and can have severe consequences if it is able to infect the nervous system. Further studies should be conducted to work against this virus and develop a vaccine, especially since it is highly common and can be virulent.

[3] Chan et. al. (2003). Epidemic Hand, Foot and Mouth Disease by Human enterovirus 71, Singapore. Emerging infectious Disease. 9. 1.
[4] Wang, Chung-Yi M.D.; Li Lu, Frank M.D.; Wu, Mei-Hwan M.D., Ph.D.; Lee, Chin-Yun M.D., Ph.D.; Huang, Li-Min M.D., Ph.D. (2004) Fatal Coxsackievirus A16 Infection. Pediatric Infectious Disease Journal. 23. 3. 275-276.
[5] Palacios, G & Oberste, MS. (2005) Enteroviruses as agents of emerging infectious diseases. Journal of Neurovirology. 11. 424-433.
[6] Phyu, Ong & Wong. (2016). A Consistent Orally-Infected Hamster Model for Enterovirus A71 Encephalomyelitis Demonstrates Squamous Lesions in the Paws, Skin and Oral Cavity Reminiscent of Hand-Foot-and-Mouth Disease. PLoS ONE 11(1).
[7] Liu LD, Zhao H, Zhang Y, Wang J, Che Y, Dong C, et al. (2011) Neonatal rhesus monkey is a potential animal model for studying pathogenesis of EV71 infection. Virology; 412:91–100.
[8] Ong KC, Wong KT. (2015) Understanding Enterovirus 71 neuropathogenesis and its impact on other neurotropic enteroviruses. Brain Pathology; 25:614–624.
[9] Ch'ng WC, Stanbridge EJ, Wong KT, Ong KC, Yusoff K, Shafee N. Immunization with recombinant enterovirus 71 viral capsid protein 1 fragment stimulated antibody responses in hamsters. Virol J 2012; 9:155
[10] Pictures of HFMD and further information from Medicine Net: http://www.medicinenet.com/hand-foot-and-mouth_syndrome/article.htm