<unk> s, also known as<unk>  jabs or<unk>  shots, are vaccines that protect against infection by<unk>  viruses. New versions of the vaccines are developed twice a year, as the<unk>  virus rapidly changes. While their effectiveness varies from year to year, most provide modest to high protection against<unk> . The United States Centers for Disease Control and Prevention (CDC) estimates that vaccination against<unk>  reduces sickness, medical visits, hospitalizations, and deaths. Immunized workers who do catch the<unk>  return to work half a day sooner on average. Vaccine effectiveness in those over 65 years old remains uncertain due to a lack of high-quality research. Vaccinating children may protect those around them. Vaccination against<unk>  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 World Health Organization (WHO) and the US Centers for Disease Control and Prevention (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 (ECDC) also recommends yearly vaccination of high risk groups. These groups include pregnant women, the elderly, children between six months and five years of age, and those with certain health problems. The vaccines are generally safe; fever occurs in five to ten percent of children vaccinated, and temporary muscle pains or feelings of tiredness may occur. In certain years, the vaccine was linked to an increase in Guillain–Barré syndrome among older people at a rate of about one case per million doses. Although most<unk> s are produced using egg proteins, they are still recommended as safe for people who have severe egg allergies, as no increased risk of allergic reaction to the egg-based vaccines has been shown for people with egg allergies. Vaccines produced using other technologies, notably recombinant vaccines and those based on cell culture rather than egg protein, started to become available from 2012 in the US, and later in Europe and Australia.<unk> s are not recommended in those who have had a severe allergy to previous versions of the vaccine itself. The vaccine comes in inactive and weakened viral forms. The<unk> e, weakened vaccine is generally not recommended in pregnant women, children less than two years old, adults older than 50, or people with a weakened immune system. Depending on the type they can be injected into a muscle, sprayed into the nose, or injected into the middle layer of the skin (intradermal). The intradermal vaccine was not available during the 2018–2019 and 2019–2020<unk>  seasons.
Influenza vaccine
Typhus vaccine
Measles vaccine
Polio vaccine
Hantavirus vaccine
MMR vaccine
Typhoid vaccine
Pertussis vaccine