Young infants cannot receive flu vaccines for safety reasons, but they can inherit passive immunity from their mother if inactivated vaccines are administered to the mother during pregnancy. Influenza vaccination also helps to reduce the probability of reassortment.In general, influenza vaccines are only effective if there is an antigenic match between vaccine strains and circulating strains. Additionally, most commercially available flu vaccines are manufactured by propagation of influenza viruses in embryonated chicken eggs, taking 6–8 months. Flu seasons are different in the northern and southern hemisphere, so the WHO meets twice a year, one for each hemisphere, to discuss which strains should be included in flu vaccines based on observation from HA inhibition assays. Other manufacturing methods include an MDCK cell culture-based inactivated vaccine and a recombinant subunit vaccine manufactured from baculovirus overexpression in insect cells. Antiviral chemoprophylaxis
Influenza can be prevented or reduced in severity by post-exposure prophylaxis with the antiviral drugs oseltamivir, which can be taken orally by those at least three months old, and zanamivir, which can be inhaled by those above seven years of age. Chemoprophylaxis is most useful for individuals at high-risk of developing complications and those who cannot receive the flu vaccine due to contraindications or lack of effectiveness. Post-exposure chemoprophylaxis is only recommended if oseltamivir is taken within 48 hours of contact with a confirmed or suspected influenza case and zanamivir within 36 hours.
Pigs become contagious within a day of infection and typically spread the virus for 7–10 days, which can spread rapidly within a herd. Pigs usually recover from infection within 3–7 days after symptoms appear. Prevention and control measures include inactivated vaccines and culling infected herds. The influenza viruses usually responsible for swine flu are IAV subtypes H1N1, H1N2, and H3N2.Some IAVs can be transmitted via aerosols from pigs to humans and vice versa. Furthermore, pigs, along with bats and quails, are recognized as a mixing vessel of influenza viruses because they have both α-2,3 and α-2,6 sialic acid receptors in their respiratory tract. Because of that, both avian and mammalian influenza viruses can infect pigs. If co-infection occurs, then reassortment is possible. A notable example of this was the reassortment of a swine, avian, and human influenza virus in 2009, resulting in a novel H1N1 strain that caused the 2009 flu pandemic. Spillover events from humans to pigs, however, appear to be more common than from pigs to humans. Other animals
Influenza viruses have been found in many other animals, including cattle, horses, dogs, cats, and marine mammals. Nearly all IAVs are apparently descended from ancestral viruses in birds. The exception are bat influenza-like viruses, which have an uncertain origin. These bat viruses have HA and NA subtypes H17, H18, N10, and N11. H17N10 and H18N11 are unable to reassort with other IAVs, but they are still able to replicate in other mammals. AIVs sometimes crossover into mammals.