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Pedro Plans. Recommendations for the Prevention and Treatment of Influenza Using Antiviral Drugs Based on Cost–Effectiveness. Expert Review of Pharmacoeconomics & Outcomes Research. Mar. 2009

 nfluenza A virus can produce sudden and unpredictable pandemics. Influenza A viruses are classified into different subtypes based on their surface glycoproteins, hemagglutinin (H) and neuraminidase (N). A total of 15 subtypes of hemagglutinin (i.e., H1–H15) and nine subtypes of neuraminidase (i.e., N1–N9) have been identified. All of these serotypes have been found in aquatic birds. Different species of wild birds form the primary natural reservoir of the influenza A virus. In humans, however, only three hemagglutinin proteins (i.e., H1, H2 and H3) and two neuraminidase proteins (i.e., N1 and N2) have been detected in epidemics and pandemics since 1900.

Since the discovery of the influenza virus, new antigenic variants of influenza A and B have continually emerged. The influenza virus changes continually by means of two mechanisms, called antigenic drift and antigenic shift.The antigenic shift is responsible for the major antigenic changes registered in human influenza A virus. The antigenic shift is produced by the reassortment of genetic components from human and nonhuman influenza viruses. The antigenic shift produces new human influenza viruses with antigenic components from the nonhuman viruses. For example, the genetic reassortment of the human influenza virus H2N1 and the avian influenza viruses H5N8 and H3N4 can produce new human influenza viruses H5N1 and H3N1, respectively. Influenza pandemics are produced by the lack of a specific immune response against the new human virus in the whole population of the world. People infected by one influenza virus develop a specific immune response against the HN strain that is unable to recognize the new viral strain.

Antiviral drugs can be used to treat influenza cases and block the spread of a new influenza pandemic in the population. The WHO recommends neuraminidase inhibitors for patients with H5N1 influenza and their contacts because oseltamivir is active against H5N1 influenza and there are no alternative treatments.Recent avian influenza outbreaks of H5N1 strains, however, were not transmitted from human to human.

Many countries are stockpiling antiviral drugs (oseltamivir) in preparation for a possible influenza pandemic. Siddiqui and Edmunds assessed the cost–effectiveness of antiviral stockpiling for the prevention and treatment of pandemic influenza in the UK.The cost–effectiveness was assessed on the assumptions of a stockpile of 14.6 million units, an attack rate of clinical influenza of 25%, mortality rates similar to those registered in 1957 and/or 1969 or the 1918 pandemics and a time-to-pandemic of 30 years. The cost–effectiveness of treating all symptomatic individuals was £1900 or £13,000 per QALY depending on the mortality. The cost–effectiveness of using a test-treatment strategy, where only laboratory-confirmed cases were treated, was associated with a cost–effectiveness ratio of £31,000 or £228,000 per QALY, depending on the mortality considered. These results demonstrate that the stockpiling of antiviral drugs for the treatment of all symptomatic patients is a cost-effective intervention.

Influenza vaccines and antiviral drugs for influenza are essential components of a comprehensive pandemic response. During a pandemic, antivirals could reduce morbidity and mortality from influenza and block transmission of influenza virus in the population. Given that the vaccine is unlikely to be available during the early months of the pandemic, antivirals will be the only intervention during the initial response. The priority groups for antiviral treatment are people at risk and people living with or caring for high-risk individuals; however, antivirals can be given to other people depending on the stockpile of antivirals.

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