at high risk of influenza-related complications or hospitalization, including people who are morbidly obese, healthy pregnant women, children aged 6–59 months, the elderly, aboriginals, and people with one of an itemized list of chronic health conditions People capable of transmitting influenza to those at high risk, including household contacts and health care workers People who provide essential community services Certain poultry workers Live attenuated influenza vaccine (LAIV) was not available in Canada for the 2019–2020 season. European Union The European Centre for Disease Prevention and Control (ECDC) recommends vaccinating the elderly as a priority, with a secondary priority people with chronic medical conditions and health care workers. The influenza vaccination strategy is generally that of protecting vulnerable people, rather than limiting influenza circulation or eliminating human influenza sickness. This is in contrast with the high herd immunity strategies for other infectious diseases such as polio and measles. This is also due in part to the financial and logistics burden associated with the need of an annual injection. United States In the United States routine influenza vaccination is recommended for all persons aged six months and over. It takes up to two weeks after vaccination for sufficient antibodies to develop in the body. The CDC recommends vaccination before the end of October, although it considers getting a vaccine in December or even later to be still beneficial. According to the CDC, the live attenuated virus (LAIV4) (which comes in the form of the nasal spray in the US) should be avoided by some groups. Within its blanket recommendation for general vaccination in the United States, the CDC, which began recommending the influenza vaccine to health care workers in 1981, emphasizes to clinicians the special urgency of vaccination for members of certain vulnerable groups, and their caregivers: Vaccination is especially important for people at higher risk of serious influenza complications or people who live with or care for people at higher risk for serious complications. In 2009, a new high-dose formulation of the standard influenza vaccine was approved. The Fluzone High Dose is specifically for people 65 and older; the difference is that it has four times the antigen dose of the standard Fluzone. The US government requires hospitals to report worker vaccination rates. Some US states and hundreds of US hospitals require health care workers to either get vaccinations or wear masks during flu season. These requirements occasionally engender union lawsuits