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.
The vaccine is marketed as Fluad in the US and was first available in the 2016–2017 flu season. The vaccine contains the MF59C.1 adjuvant which is an oil-in-water emulsion of squalene oil. It is the first adjuvanted seasonal flu vaccine marketed in the United States. It is not clear if there is a significant benefit for the elderly to use a flu vaccine containing the MF59C.1 adjuvant. Per Advisory Committee on Immunization Practices guidelines, Fluad can be used as an alternative to other influenza vaccines approved for people 65 years and older.Vaccinating health care workers who work with elderly people is recommended in many countries, with the goal of reducing influenza outbreaks in this vulnerable population. While there is no conclusive evidence from randomized clinical trials that vaccinating health care workers helps protect elderly people from influenza, there is tentative evidence of benefit.Fluad Quad was approved for use in Australia in September 2019, Fluad Quadrivalent was approved for use in the United States in February 2020, and Fluad Tetra was approved for use in the European Union in May 2020. Pregnancy
As well as protecting mother and child from the effects of an influenza infection, the immunization of pregnant women tends to increase their chances of experiencing a successful full-term pregnancy.The trivalent inactivated influenza vaccine is protective in pregnant women infected with HIV. Safety
Side effects
Common side effects of vaccination include local injection-site reactions and cold-like symptoms. Fever, malaise, and myalgia are less common.