インフルエンザの予防接種は強制ですか？
Influenza vaccines, also known as flu shots or flu jabs, are vaccines that protect against infection by influenza viruses. A new version of the vaccine is developed twice a year, as the influenza virus rapidly changes. While their effectiveness varies from year to year, most provide modest to high protection against influenza. The United States Centers for Disease Control and Prevention (CDC) estimates that vaccination against influenza reduces sickness, medical visits, hospitalizations, and deaths. When an immunized worker does catch the flu, they are on average back at work a half day sooner. Vaccine effectiveness in those under two years old and over 65 years old remains unknown due to the low quality of the research. Vaccinating children may protect those around them.
The World Health Organization (WHO) and the CDC recommend yearly vaccination for nearly all people over the age of six months, especially those at high risk. The European Centre for Disease Prevention and Control also recommends yearly vaccination of high risk groups. These groups include pregnant women, the elderly, children between six months and five years of age, those with other health problems, and those who work in healthcare.
The vaccines are generally safe. Fever occurs in five to tenpercent of children vaccinated. Temporary muscle pains or feelings of tiredness may occur as well. In certain years, the vaccine has been linked to an increase in Guillain–Barré syndrome among older people at a rate of about one case per million doses. It should not be given to those with severe allergies to previous versions of the vaccine. Although most influenza vaccines are produced using egg-based techniques, influenza vaccines are nonetheless recommended for people with egg allergies, even if severe. The vaccines come in both "inactive" and "weakened" viral forms. The inactive version should be used for those who are pregnant. They come in forms that are injected into a muscle, sprayed into the nose, or injected into the middle layer of the skin.
Vaccination against influenza began in the 1930s with large scale availability in the United States beginning in 1945. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale price in the developing world is about $5.25 USD per dose as of 2014. In the United States, it costs less than $25 USD as of 2015.

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