Avian Influenza: a global threat needing a global solution

Since the 1700s, there have been ten to thirteen influenza outbreaks or probable pandemics, of which three have occurred since the beginning of the 20th century: the 1918–1919 Spanish flu pandemic, the 1957–1958 Asian flu pandemic and the 1968–1969 Hong Kong flu pandemic [1]. Of the three pandemics, the 1918–1919 pandemic was the most severe. The 1918–1919 strain of influenza was unusual because of the high rate of mortality among victims between the ages of 15 and 35 years. Deaths from influenza are usually due to secondary bacterial infection but many deaths during the 1918–1919 pandemic were caused directly by the virus itself. It appears that the immune system in young persons paradoxically went into over-drive while battling the influenza virus and progressed into an immunologic storm that killed the victims [2]. This was in contrast to the pandemics of 1957–1958 and 1968–1969 which were much milder. There were several reasons for this: the influenza strains were less virulent, the patterns of mortality were more typical of a usual seasonal influenza outbreak (i.e. it was concentrated among the very young and very old) and doctors were able to use antibiotics to treat secondary bacterial infections. The Attack Rate is the percentage of the population that becomes ill from an infection while case fatality rate refers to the percentage of infected people who die from the infection. Experts generally agree that the attack rates of the past 3 influenza outbreaks in the last century did not differ markedly and is estimated to be 25% to 30%. Using similar evidence, experts estimate the case fatality rate during the 1918 outbreak to be about 2.5% whereas the case fatality rates during the 1957–1958 and 1968–1969 episodes were below 0.2% [3].The genes of the influenza virus can mutate in 2 main ways: (1) antigenic drift which involves small errors being incorporated into a virus gene sequence when the virus makes copies of itself and (2) antigenic shift involving an ex