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In recent years there has been a steady increase in the number of people who distrust the use of vaccines to prevent disease.  As a consequence, previously controlled diseases have re-emerged across the world. Shockingly, research by the Center for Disease Control and Prevention (CDC) has discovered “the percentage of 2-year-olds who have never received a single vaccination has quadrupled since 2001, reaching 1.3 percent of children born in 2015” (Hill HA 2018). This vaccine hesitancy in parents facilitates the global spread of illnesses through young children; illnesses that could potentially be controlled among large populations.  Recent outbreaks of disease have led the World Health Organization to declare this vaccine hesitancy “among the top 10 health threats worldwide, alongside Ebola, H.I.V. and drug-resistant infections” (Ten Threats 2019). Consequently, research is being done in order to determine the exact link between children receiving various vaccinations and improvements in health. 

One developed population that has been the subject of very little study in regards to vaccinations is the nation of Japan.  Due to the increased likelihood of spreading illness, the World Health Organization has largely recommended that children under the age of six receive the influenza vaccine. Despite this recommendation in Japan, the vaccine has not seen widespread application.  This is due to many factors including the requirement that it be administered by medical institutions. An additional roadblock to receiving the vaccine is that it is only subsidized by a few employee health care plans, and is mostly given at the patient’s expense. Japan is one of very few developed nations that lacks a national vaccine registry, so medical records regarding the amount of shots administered can only be accessed on the local level. Because of these setbacks, the only prior studies that have been conducted on influenza vaccination have been in the form of case studies of smaller, regional populations, rather than the country as a whole.    

Research on influenza vaccinations in Japan is relevant on an international scale because of increasing vaccine hesitancy worldwide. If vaccinations are irrefutably determined to be effective in preventing illness, it may be possible for research institutions to reduce distrust, thereby alleviating an international health threat. Influenza is a good candidate to begin research to test this theory because it has a presence in a large portion of the world. The CDC estimates that since 2010, “influenza has resulted in between 9.3 and 49.0 million illnesses” on an international scale (Burden of Influenza, 2020). The resulting impact is the death of nearly 79,000 people, a figure that will continue to rise if distrust for vaccines continues to expand. 

Researchers in Japan endeavored to conduct a study on a nationwide scale to determine the effectiveness of the influenza vaccine administered by medical institutions. The ultimate goal of the research was to determine whether or not flu vaccines successfully prevented contraction of the illness, as well as secondary effects of the flu, including pneumonia and bacterial sinusitis (Shibata N. 2018). 

The study was designed and implemented by five prestigious researchers; N. Shibata, S. Kimura, T. Hoshino, M. Takeuchi, and H. Urushihara. Funding for this study was provided in part by the MEXT- supported Program for the Strategic Research Foundation and Private Universities.  Donors did not have any input into methods design, collection of data, or the choice to publish findings in a scientific journal. The only potential conflict of interest for this study was that one researcher, S. Kimura, is a director for the Japan Medical Data Center Co. Ltd., which provided data utilized in the study.  No other authors reported any conflicts of interest. 

In order to determine the effectiveness of the influenza vaccination, data was obtained from a large-scale claims database which provided information for nearly three million people receiving employee healthcare, along with their dependents (Shibata N. 2018). This data was originally collected by the Japan Medical Data Center Co. Ltd.  Because children are regarded as the primary candidates for spreading contagious illnesses, they were deemed the focus of the study. Data was monitored for all children aged one through fifteen who were claimed as dependents on employee-based healthcare plans within this database. In order to guarantee privacy for these underage participants, special randomized codes were given to the children in place of their names on records. 

Researchers studied four consecutive influenza seasons dating from October 2010 to May 2014.  The duration of the flu season was defined as the time from when the first vaccine was administered each year on October 1st, to the time when less than one case of influenza was reported each week to the National Institute of Infectious Diseases, typically around the end of May. In total, researchers studied a population of approximately 116,000 children over the four flu seasons (Shibata N. 2018).  The rate at which children were vaccinated varied by age and gender across the four years. Records in the researchers’ database included vital information, such as whether or not the patient received a vaccine, as well as documentation from doctor’s visits and pharmacy benefits. Standards for diagnosis of influenza were held constant throughout the study, utilizing the International Statistical Classification of Diseases and Related Health Problems 10th Revision (ICD-10) codes, ensuring all patients were diagnosed by the same standards throughout the four seasons. If a child in the database contracted the flu, follow up research was conducted to monitor the presence of secondary illnesses related to influenza. 

The study ultimately confirmed that the influenza vaccination was successful in preventing contraction of the illness over the time period of study.  Additionally, there were decreased rates in the number of children who suffered from secondary ailments after receiving the vaccination. Researchers presented their data in the form of odds ratios, which are represented as values between the numbers zero and two. If the odds ratio between two variables is one, the presence of the first variable has no influence on the second variable.  If the value is less than one, it can be concluded that the presence of the first variable reduces the likelihood of the second variable occurring. If the value is greater than one, it is believed that the presence of the first variable increases the likelihood of the second variable being present. In this study, the presence of vaccinations influenced the likelihood of the flu appearing with an odds ratio between 0.811 and 0.889. With an odds ratio of less than one, this statistic suggests that vaccines result in fewer cases of influenza. Additionally, odds ratios were calculated to portray the likelihood of contracting a secondary illness following the flu for patients receiving the flu shot.  These ratios were much lower, ranging from 0.541 to 0.626 for the most common secondary ailment, pneumonia (Shibata N. 2018). This indicates that vaccines reduce the odds of getting an additional illness.  

One potential flaw in this study is the specificity of the participant group. Due to the limitations of the database, the researchers were only able to study the children of employees receiving health insurance from their employers.  One might argue that this is not representative of an entire population. There was no guarantee that the sample was taken from a variety of geographic areas, allowing the possibility that there could have been an area of the nation affected by a different strain of the flu not represented in this research.

Ultimately, this study provides strong evidence that the influenza vaccination is successful in reducing the likelihood of children contracting the flu. These results support the argument that children should receive immunizations to prevent the spread of contagious disease, at least in the case of influenza. Additional studies can build off of this research and expand to other illnesses, alleviating distrust in vaccinations for future populations. 



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Shibata N, Kimura S, Hoshino T, Takeuchi M, Urushihara H. 2018. Effectiveness of influenza

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Ten threats to global health in 2019. 2019. World Health Organization; [accessed 2020 Feb 4].






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