<P> 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 . </P> <P> The vaccines are generally safe . Fever occurs in five to ten percent 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 . </P> <P> 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 . </P> <P> The CDC recommends the flu vaccine as the best way to protect people against the flu and prevent its spread . The flu vaccine can also reduce the severity of the flu if a person contracts a flu strain that the vaccine did not contain . It takes about two weeks following vaccination for protective antibodies to form . </P>

When did the flu shot first come out
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