virus. In short, this one amino acid difference in the NS1 protein produced by the NS RNA molecule of the H5N1 virus is believed to be largely responsible for an increased pathogenicity (on top of the already increased pathogenicity of its hemagglutinin type which allows it to grow in organs other than lungs) that can manifest itself by causing a cytokine storm in a patient's body, often causing pneumonia and death. Treatment Neuraminidase inhibitors are a class of drugs that includes zanamivir and oseltamivir, the latter being licensed for prophylaxis treatment in the United Kingdom. Oseltamivir inhibits the influenza virus from spreading inside the user's body. It is marketed by Roche as Tamiflu. This drug has become a focus for some governments and organizations trying to be seen as making preparations for a possible H5N1 pandemic. In August 2005, Roche agreed to donate three million courses of Tamiflu to be deployed by the WHO to contain a pandemic in its region of origin. Although Tamiflu is patented, international law gives governments wide freedom to issue compulsory licenses for life-saving drugs. A second class of drugs, which include amantadine and rimantadine, target the M2 protein, but have become ineffective against most strains of H5N1, due to their use in poultry in China in the 1990s, which created resistant strains. However, recent data suggest that some strains of H5N1 are susceptible to the older drugs, which are inexpensive and widely available. Research indicates that therapy to block one cytokine to lessen a cytokine storm in a patient may not be clinically beneficial. Mortality rate From the first laboratory-confirmed case through November 21, 2016, the number of confirmed human cases of H5N1 reported to WHO stands at 856, with 452 fatalities, reflecting a 53% fatality rate. The global case fatality ratio looks only to the official tally of cases confirmed by the WHO. It takes no account of other cases, such as those appearing in press reports. Nor does it reflect any estimate of the global extent of mild, asymptomatic, or other cases which are undiagnosed, unreported by national governments to the WHO, or for any reason cannot be confirmed by the WHO. While the WHO's case count is clearly the most authoritative, these unavoidable limitations result in an unknown number of cases being omitted from it. Notes and references See also Fujian flu Severe acute respiratory syndrome Further reading Epidemiology Influenza A