Influenza vaccine

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. 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 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. 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, the vaccine costs less than $25 USD per dose, as of 2015. 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 strain that the vaccine did not contain. It takes about two weeks following vaccination for protective antibodies to form. A 2012 meta-analysis found that flu vaccination was effective 67 percent of the time; the populations that benefited the most were HIV-positive adults ages 18 to 55 (76 percent), healthy adults ages 18 to 46 (approximately 70 percent), and healthy children ages six to 24 months (66 percent). A vaccine is assessed by its efficacy – the extent to which it reduces risk of disease under controlled conditions – and its effectiveness – the observed reduction in risk after the vaccine is put into use. In the case of influenza, effectiveness is expected to be lower than the efficacy because it is measured using the rates of influenza-like illness, which is not always caused by influenza. Influenza vaccines generally show high efficacy, as measured by the antibody production in animal models or vaccinated people. However, studies on the effectiveness of flu vaccines in the real world are difficult; vaccines may be imperfectly matched, virus prevalence varies widely between years, and influenza is often confused with other influenza-like illnesses. However, in most years (16 of the 19 years before 2007), the flu vaccine strains have been a good match for the circulating strains, and even a mismatched vaccine can often provide cross-protection. The virus rapidly changes due to antigenic drift, a slight mutation in the virus that causes a new strain to arise. Trials of both live and inactivated influenza vaccines against seasonal influenza have been summarized in several meta-analyses. Studies on live vaccines have very limited data, but these preparations may be more effective than inactivated vaccines. The meta-analyses examined the efficacy and effectiveness of inactivated vaccines against seasonal influenza in adults, children, and the elderly. Tom Jefferson, who has led Cochrane Collaboration reviews of flu vaccines, has called clinical evidence concerning flu vaccines 'rubbish' and has therefore declared them to be ineffective; he has called for placebo-controlled randomized clinical trials, which most in the field hold as unethical. His views on the efficacy of flu vaccines are rejected by medical institutions including the CDC and the National Institutes of Health, and by key figures in the field like Anthony Fauci.