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 […]

H1N1 vaccines

How safe are H1N1 vaccines? A wide range of measures are in place to monitor and review the safety of H1N1 pandemic vaccines, including (pre-)clinical testing, regulatory assessment, and wide-scale monitoring. This builds on the extensive safety record established with seasonal influenza vaccines over the last 60 years in a wide range of age and […]

Similarities between Swine and Spanish flu

It is interesting to note that there are several similarities between the ‘Swine flu’ threat and the ‘Spanish flu’: Both were caused by an H1N1 virus that originally came from birds, but probably was transmitted to humans via pigs in America. Both caused relatively mild disease and little mortality in the first months of their […]

Spread of H1N1 virus

From spring 2009 onwards, a new influenza A virus of the H1N1 subtype started to circulate among humans in Mexico. Tens of thousands were infected before the virus spread to Texas and California, where it was first identified as a new human virus that probably had originated from pigs. The virus had initially not been […]

Origin of H1N1 (‘Mexican’ or ‘Swine’ flu)

The accompanying graph reveals the origin of the ‘Swine flu virus’ as deduced from sequence analysis of the respective genome segments, that through a process of so-called “re-assortment” shaped the new virus. All the eight segments originate from avian influenza A viruses that were introduced into pigs directly from birds or through a human intermediate […]

Pandemic alert phases

The World Health Organization (WHO) has developed an alert system to help inform the world about the development of the different stages towards a pandemic. The alert system is comprised of six phases. The current situation with the HPAI-H5N1 virus in animals and humans places the world in pandemic alert phase 3. This means that […]

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 […]

A pandemic influenza vaccine

To prepare the world for the next influenza pandemic, the WHO has advised national governments to develop pandemic preparedness plans. The production, distribution and administration of a pandemic influenza vaccine play a major role in such plans. Pandemic influenza vaccines would reduce spreading of the virus and the burden of disease in the population, like […]


There are in principle two types of seasonal influenza vaccines. The first is the traditional flu shot, which is an inactivated vaccine that does not contain live virus. It is given by injection, usually in the upper arm muscle. Inactivated vaccines are available in three forms: whole-virus, split-virus, and subunit-virus vaccines. Whole-virus vaccines are classically […]