has concluded that there is no evidence of toxicity from thiomersal in vaccines and no reason on grounds of safety to change to more-expensive single-dose administration. Types Seasonal flu vaccines are available either as: a trivalent or quadrivalent intramuscular injection (IIV3, IIV4, or RIV4, that is, TIV or QIV), which contains the inactivated form of the virus a nasal spray of live attenuated influenza vaccine (LAIV, Q/LAIV), which contains the live but attenuated (weakened) form of the virus. TIV or QIV induce protection after injection (typically intramuscular, though subcutaneous and intradermal routes can also be protective) based on an immune response to the antigens present on the inactivated virus, while cold-adapted LAIV works by establishing infection in the nasal passages. Recommendations Various public health organizations, including the World Health Organization (WHO), recommend that yearly influenza vaccination be routinely offered, particularly to people at risk of complications of influenza and those individuals who live with or care for high-risk individuals, including: people aged 50 years of age or older people with chronic lung diseases, including asthma people with chronic heart diseases people with chronic liver diseases people with chronic kidney diseases people who have had their spleen removed or whose spleen is not working properly people who are immunocompromised residents of nursing homes and other long-term care facilities health care workers (both to prevent sickness and to prevent spread to their patients) children and adolescents (aged 6 months through 18 years) who are receiving aspirin- or salicylate-containing medications and who might be at risk for experiencing Reye syndrome after influenza virus infection American Indians/Alaska Natives people who are extremely obese (body mass index ≥40 for adults) The flu vaccine is contraindicated for those under six months of age and those with severe, life-threatening allergies to flu vaccine or any ingredient in the vaccine. World Health Organization , the World Health Organization (WHO) recommends seasonal influenza vaccination for: First priority: Pregnant women Second priority (in no particular order): Children aged 6–59 months Elderly Individuals with specific chronic medical conditions Health-care workers Canada The National Advisory Committee on Immunization (NACI), the group that advises the Public Health Agency of Canada, recommends that everyone over six months of age be encouraged to receive annual influenza vaccination, and that children between the age of six months and 24 months, and their household contacts, should be considered a high priority for the flu vaccine. Particularly: People