These reactions likely result from hypersensitivity to vaccine components, one of which is residual egg protein. These local injection-site reactions are slightly more common with vaccine administered intradermally, with needle-free jet injection and with high-dose IIV.

Katherine Roguski, Alicia FryInfluenza is caused by infection of the respiratory tract with influenza viruses, RNA viruses of the Influenza viruses spread from person to person, primarily through respiratory droplet transmission (such as when an infected person coughs or sneezes near a susceptible person).

However, it is uncommon for people with less severe illness to be tested for A(H5N1) or A(H7N9) viruses.Influenza can be difficult to distinguish from respiratory illnesses caused by other pathogens on the basis of signs and symptoms alone. Government of Canada and British Columbia confirm case of H7N9 avian influenza in Canada; HPV immunization program expanded to vulnerable boys; Internet-based service makes it easier to test for STIs, HIV and Hep C; Measles outbreak in 2010 traced to Winter Olympics visitors; Meningococcal disease among Scouts attending the 23rd World Scout Jamboree in Japan ; Multilingual videos … If there is an increased risk of GBS after seasonal influenza vaccines, it is small, approximately 1–2 additional cases per 1 million people vaccinated.The most frequent side effects of LAIV reported in healthy adults include minor upper respiratory symptoms, runny nose, and sore throat, which are generally well tolerated. Fever, malaise, myalgia, headache, and other systemic symptoms sometimes occur after vaccination; these may be more frequent in people with no previous exposure to the influenza virus antigens in the vaccine (such as young children) and are generally short-lived.Guillain-Barré syndrome (GBS) was associated with the 1976 swine influenza vaccine, with an increased risk of 1 additional case of GBS per 100,000 people vaccinated.

CDC estimates that from 2010 through 2014, approximately 9.2–35.6 million symptomatic infections, 4.2–16.7 million outpatient visits, 139,000–708,000 hospitalizations, and 12,000–56,000 deaths associated with influenza viruses occurred each year in the United States (Influenza A viruses not only circulate among humans but also among many animal species populations, although influenza B viruses circulate widely only among humans.

The decision to start antiviral treatment should not be delayed while waiting for results of confirmatory laboratory testing.Early antiviral treatment can shorten the duration of fever and other symptoms and reduce the risk of complications from influenza. For hospitalized patients, those with severe illness, or those at higher risk of complications, antiviral therapy may still be beneficial if started >48 hours after illness onset.

Infected birds shed avian influenza virus in their saliva, mucus, and droppings, and transmission to humans can occur directly (through touching an infected animal or droplet spread) or indirectly (through inhalation of these viruses in the air or through fomite transmission on infected surfaces). Reported human infections with avian influenza A(H5N1) or A(H7N9) viruses often have severe pneumonia or respiratory failure and a high case-fatality ratio.