What is pandemic influenza

Influenza viruses are changing continuously and new strains emerge from time to time. If a new influenza virus subtype, that is very different from all previous viruses, emerges and causes disease in the human population, people will have little or no specific immunity to it, and consequently this virus may spread quickly and become a […]

How they work

When a person is exposed to an influenza virus, the innate and subsequently the adaptive or specific immune response kicks in and provides defence against the invading virus. Depending on the nature of the virus and the effectiveness of the immune response, the infected individual suffers from more or less severe consequences of the influenza […]

Pandemics in the 20th century

When a new influenza virus appears, against which the human population has no immunity, a pandemic may occur. This happened in 1918 (the “Spanish flu”, caused by an H1N1 subtype), in 1957 (the “Asian flu” caused by an H2N2 subtype) and in 1968 (the “Hong Kong flu”, caused by an H3N2 subtype). Of all pandemics, […]

How do pandemics Occur

An influenza pandemic is a global outbreak of influenza and occurs when a new influenza virus emerges, spreads and causes disease worldwide. Influenza A viruses continuously undergo antigenic evolution. There are two main mechanisms by which they do so: antigenic drift causes regular influenza epidemics, while antigenic shift is the cause of occasional global outbreaks […]


Influenza A viruses continuously undergo antigenic evolution. Since the viral surface glycoprotein HA is the antigen against which virus-neutralizing antibodies are directed, it is primarily the antigenic variation of HA that is responsible for the immune escape of influenza viruses. Two distinct mechanisms of antigenic evolution can be identified: antigenic drift causes regular influenza epidemics, […]