The influenza virus causes seasonal epidemics. Vaccines protect against infectious diseases by preparing the immune system to fight off specific pathogens. The influenza vaccine works by introducing components of the virus, prompting the immune system to produce antibodies that can defend against future infections. This protective measure has evolved, becoming a tool in managing seasonal flu.
Early Development of the Flu Vaccine
The journey to develop a flu vaccine began with scientific discoveries about influenza. For many years, the illness was mistakenly attributed to a bacterium, Haemophilus influenzae. A pivotal breakthrough occurred in 1933 when British scientists Wilson Smith, Christopher Andrewes, and Patrick Laidlaw isolated the influenza A virus from human samples, identifying its viral cause.
This isolation opened new avenues for research, propelled by the devastating 1918 flu pandemic. Scientists began to explore methods for growing the virus in laboratory settings, with a significant advancement made by Ernest William Goodpasture and colleagues in 1931, who reported viral growth in embryonated hens’ eggs. This technique became fundamental for vaccine production, as researchers like Jonas Salk and Thomas Francis Jr. at the University of Michigan, with support from the U.S. Army, utilized it to develop the first inactivated influenza vaccine.
The initial monovalent vaccine, targeting a single strain of influenza A, was first used to inoculate U.S. defense forces during World War II, starting around 1938. The discovery of influenza B virus in 1940 led to the development of a bivalent vaccine in 1942, protecting against both influenza A and B strains. This inactivated influenza vaccine was licensed for civilian use in the United States in 1945.
From Lab to Widespread Use
Following initial successes, the influenza vaccine transitioned to a broadly administered public health intervention. Mass production relied on the egg-based method, which remains a primary technique for many flu vaccines today. A challenge in influenza vaccination is the virus’s ability to constantly change through antigenic drift, necessitating annual vaccine updates.
To address this evolution, the World Health Organization (WHO) established the Worldwide Influenza Centre in 1948 and the Global Influenza Surveillance and Response System (GISRS) in 1952. These systems monitor circulating flu strains globally, providing recommendations for vaccine composition, with annual guidance for the Northern and Southern Hemispheres. Over the decades, various vaccine types have emerged, including split and subunit vaccines in the 1960s, designed to reduce adverse reactions. The first trivalent vaccines, protecting against two influenza A strains and one influenza B strain, were introduced in 1978.
Further advancements led to the licensing of the live attenuated influenza vaccine (LAIV), administered as a nasal spray, in 2003. By 2012, quadrivalent vaccines became available, offering protection against two influenza A and two influenza B strains. Recombinant protein vaccines, which do not use eggs or live viruses in their production, received approval in 2013, diversifying manufacturing options. These refinements and global surveillance have integrated the flu vaccine into public health strategies, with recommendations for annual vaccination for individuals six months and older becoming common practice.