The 1918 Spanish flu pandemic was caused by a particularly virulent strain of influenza virus. It infected 500 million people, caused around 50 million deaths, and its impact was so severe that global life expectancy fell dramatically. It claimed more lives than the First World War.
In their efforts to develop a vaccine, researchers at the time worked under the mistaken assumption that influenza was caused by bacteria, based on Richard Pfeiffer’s 1892 discovery of the “bacillus influenzae”, which today is known as the bacterium Haemophilus influenzae.
It was not until 1931 that Richard Shope discovered the Influenza A virus in pigs. In 1933, Wilson Smith, Christopher Andrewes and Patrick Laidlaw then discovered the same virus in humans.
Subsequent work has described different versions of the virus surface proteins haemagglutinin (HA) and neuraminidase (NA). Different combinations of these give rise to the influenza A virus subtypes, including the H1N1, H2N2 and H3N2 subtypes that have afflicted humankind for over 100 years.
The first inactivated influenza vaccine for use in humans was developed by Thomas Francis (who also developed the Influenza B virus in 1940) and his student Jonas Salk, who later developed the polio vaccine.
The influenza vaccine was tested for safety and efficacy in the US military during World War II before being licensed for wider use in 1945. However, researchers soon realised that the virus regularly mutated, meaning vaccines needed annual updates to remain effective.
Constant evolution
Various technologies and methods are used in producing flu vaccines. In the northern hemisphere, design for the autumn vaccine begins in February, and is based on the strains circulating at that time.
Over recent decades, vaccines have evolved in response to changes in circulating viruses. In 1948, the World Health Organization (WHO) established the Global Influenza Programme and, in 1952, the Global Influenza Surveillance and Response System (GISRS) to track emerging strains.
These initiatives enabled the production of seasonally updated vaccines, and form the basis for the WHO’s annual recommendation of specific strains to be included in each hemisphere’s immunisations against Influenza A H1N1 and H3N2, as well as Influenza B viruses.
Flu returns annually as an epidemic. It is a constant threat to public health, affecting millions of people and causing severe complications in the most vulnerable: young children, older adults, and people with pre-existing conditions.
