The treatment of influenza with antiviral drugs

Abstract

Influenza vaccination with current inactivated vaccines homologous to the prevalent wild-type virus can reduce influenza illness in 75%-80% of healthy adults. Vaccine is recommended for all individuals with chronic underlying diseases and for those aged 65 years or older. Although influenza vaccination is still advocated for patients with blunted immunity, protection rates are not as high, running at 40% for frail institutionalized elderly people. The influenza antiviral agents amantadine or rimantadine, zanamivir and oseltamivir can modify the severity of illness and reduce the duration of illness by about 1.5-2.5 days. Amantadine inhibits only influenza A. Resistant virus may emerge in up to 33% of amantadine-treated patients in the first 5 days of treatment and be transmitted to susceptible close contacts. Side effects are usually mild in short courses of treatment. The neuraminidase inhibitor drugs zanamivir and oseltamivir act on both influenza A and B. Treatment is most effective when given within 30-36 hours after the onset of illness, and the earlier the better. Influenza should be treated with antiviral drugs in unvaccinated and vaccinated high-risk patients, as well as immunosuppressed patients with influenza-like illness, in periods of confirmed influenza prevalence. These drugs may be of great value in the event of a major viral antigenic shift that causes pandemic influenza, if an adequate supply can be sustained.

Fig. 1: Schematic representation of influenza virus attachment, internalization, replication and exit from the host respiratory cell and steps inhibited by antiviral drugs. Amantadine blocks viral internalization and uncoating. Neuraminidase inhibitors prevent the neuraminadase from releasing budding viruses and dispersing virions. Photo: Myra Rudakewich

Fig. 2: An algorithm for the treatment of acute influenza-like illness (ILI). *Influenza virus outbreak confirmed by public health authorities. †Influenza antiviral treatment could be considered. It could also be considered in relatively healthy unvaccinated people aged less than 65 years to minimize absence from work. Photo: Myra Rudakewich