DISCOVERIES & BREAKTHROUGHS
Before the 20th century, influenza was a mystery. At the time, people believed it was caused by a bacterium. Thanks to new research and scientific breakthroughs during the 20th century, we have solved many of the mysteries that influenza has been keeping for so long.
Up until the 20th century, not much was known about influenza. At the time, people believed that a bacterium called Pfeiffer's bacillus was the cause of influenza. The Spanish Flu of 1918 started a continuous influenza investigation that helped to change the way people thought about influenza forever.
After the Spanish Flu died down in 1919, a small group of microbiologists was determined to learn more about influenza. By the end of the 1920s, the theory that influenza was caused by bacteria was abandoned; researchers hypothesized that a virus caused influenza. And so the search for a virus began. In 1930, a strain of the swine flu was isolated and scientists later isolated a strain of human influenza several years later. Dr. Thomas Francis, a celebrated researcher at the University of Michigan, discovered influenza A viruses in 1936 and later discovered influenza B viruses in 1940.
During the 1940s, Dr. Francis and Jonas Salk, who later pioneered the polio vaccine, created the first flu vaccine. This vaccine was made using a new method, in which flu viruses were grown in fertilized chicken eggs and harvested to make flu vaccine. The vaccine worked successfully for several years, but during the flu season of 1946-47, the vaccine failed to prevent flu infection. New flu strains appeared often, and researchers soon realized that they had to update flu vaccines every year to keep up. Meanwhile, the newly formed WHO (World Health Organization) set up a world influenza center in London, led by researcher Sir Christopher Andrewes. Every year, affiliated labs from around the world sent unknown influenza strains to the influenza center in London, where scientists would identify them. After careful consideration, WHO sent drug manufacturers a list of candidate strains to use for the next years flu vaccine.
As technology improved, biologists continued learning more about influenza. After 1968, virologists were able to see the differences between the HA and NA molecules for the first time. They also discovered that NA and HA molecules mutated independently and that genetic reassortment, or antigenic shift, was largely responsible for new subtypes that emerged. However, scientists still did not know the true origin of influenza viruses. That all changed in 1974, when researchers revealed that the intestines of aquatic birds was the natural home of influenza viruses. Eventually, scientists identified 15 different types of HA molecules and 9 different types of NA molecules, leaving room for a hypothetical 135 possible flu subtypes.