Oseltamivir and zanamivir are effective for prophylaxis and post-exposure prophylaxis, and research overall indicates that NA inhibitors are effective at reducing rates of complications, hospitalization, and mortality and the duration of illness. Additionally, the earlier NA inhibitors are provided, the better the outcome, though late administration can still be beneficial in severe cases. Other NA inhibitors include laninamivir and peramivir, the latter of which can be used as an alternative to oseltamivir for people who cannot tolerate or absorb it.The adamantanes amantadine and rimantadine are orally administered drugs that block the influenza viruss M2 ion channel, preventing viral uncoating. These drugs are only functional against IAV but are no longer recommended for use because of widespread resistance to them among IAVs. Adamantane resistance first emerged in H3N2 in 2003, becoming worldwide by 2008. Oseltamivir resistance is no longer widespread because the 2009 pandemic H1N1 strain (H1N1 pdm09), which is resistant to adamantanes, seemingly replaced resistant strains in circulation. Since the 2009 pandemic, oseltamivir resistance has mainly been observed in patients undergoing therapy, especially the immunocompromised and young children. Oseltamivir resistance is usually reported in H1N1, but has been reported in H3N2 and IBVs less commonly. Because of this, oseltamivir is recommended as the first drug of choice for immunocompetent people, whereas for the immunocompromised, oseltamivir is recommended against H3N2 and IBV and zanamivir against H1N1 pdm09. Zanamivir resistance is observed less frequently, and resistance to peramivir and baloxavir marboxil is possible. Prognosis
In healthy individuals, influenza infection is usually self-limiting and rarely fatal.
Both lineages are in circulation in humans, disproportionately affecting children. IBVs contribute to seasonal epidemics alongside IAVs but have never been associated with a pandemic.ICV, like IBV, is primarily found in humans, though it also has been detected in pigs, feral dogs, dromedary camels, cattle, and dogs. ICV infection primarily affects children and is usually asymptomatic or has mild cold-like symptoms, though more severe symptoms such as gastroenteritis and pneumonia can occur. Unlike IAV and IBV, ICV has not been a major focus of research pertaining to antiviral drugs, vaccines, and other measures against influenza. ICV is subclassified into six genetic/antigenic lineages.IDV has been isolated from pigs and cattle, the latter being the natural reservoir. Infection has also been observed in humans, horses, dromedary camels, and small ruminants such as goats and sheep. IDV is distantly related to ICV. While cattle workers have occasionally tested positive to prior IDV infection, it is not known to cause disease in humans. ICV and IDV experience a slower rate of antigenic evolution than IAV and IBV. Because of this antigenic stability, relatively few novel lineages emerge. Genome and structure
Influenza viruses have a negative-sense, single-stranded RNA genome that is segmented. The negative sense of the genome means it can be used as a template to synthesize messenger RNA (mRNA). IAV and IBV have eight genome segments that encode 10 major proteins. ICV and IDV have seven genome segments that encode nine major proteins.