What Is the History of Flu Vaccine Development?
In 1933, researchers discovered that viruses (influenza virus types A, B, and rarely C) cause influenza (flu). Prior to 1933, people thought a bacterium named Haemophilus influenzae caused the flu. In 1938, Jonas Salk and Thomas Francis developed the first vaccine against flu viruses. This first flu vaccine protected the U.S. military forces against the flu during World War II. Dr. Salk used his experience with influenza vaccine to develop an effective polio vaccine in 1952. Vaccines produced from the 1940s to the 1960s were not as purified as more modern vaccines, and the impurities in vaccines were thought to contribute to side effects such as fever, aches, and fatigue. Since these symptoms were similar to those that accompanied the flu (flu symptoms usually were more severe and lasted longer), people mistakenly thought they got the flu from the vaccination. However, they did not get the flu from the vaccines since the vaccines used killed virus.
In a public vaccination program designed to prevent a pandemic swine flu outbreak in 1979, about 25% of people in the United States received flu vaccinations. Unfortunately, the 1979 vaccine was associated with a small increased risk of Guillain-Barré syndrome, a serious neurological condition, with the risk estimated to be one to nine excess cases per million doses of vaccine, but no cause for this increase in risk was ever discovered. Fortunately, no pandemic developed, and the vaccination program for that flu virus was cancelled. Since that time, researchers have improved vaccine purification, and millions of people have continued to be vaccinated every year. Currently, influenza viruses are inoculated into eggs, where they multiply; afterward, they are harvested and separated from most egg particles and egg antigens, but some people who have an egg allergy may get a reaction to such a flu vaccination; however, most people who have a mild egg allergy usually have no reaction to the vaccines. Attenuated viruses (for nasal sprays like FluMist) are grown similarly, but strains are selected that only replicate under cool or cold temperatures so they can survive in the cool nasal passages long enough to stimulate an immune response but do not easily replicate and spread to warmer body regions like the lungs.
Because of the potential for widespread infection, life-threatening complications, and deaths that the H1N1 pandemic virus strain seemed to possess, health researchers accelerated the H1N1 tests so that the vaccine could be provided before the usual six-month timeline. However, all of the steps (cultivation, safety, efficacy, approval, and distribution) were done in the same way as for seasonal vaccines but over a shorter period with fewer people involved in the initial trials. Tested and approved H1N1 vaccine started to become available in late September 2009 (in Europe) and in October 2009 in the Americas and Asia.
A major change in terminology (naming conventions or abbreviations for influenza vaccines) occurred in the 2014-2015 vaccine year. Since then, vaccine abbreviations have continued to change. The new terminology (abbreviations) are as follows, according to the CDC in 2019-2020:
- IIV = Inactivated Influenza Vaccine
- IIV3 = Trivalent Inactivated Influenza Vaccine
- IIV4 = Quadrivalent Inactivated Influenza Vaccine
- RIV4 = Quadrivalent Recombinant Influenza Vaccine
- LAIV4 = Quadrivalent Live Attenuated Influenza Vaccine
- aIIV3 refers specifically to adjuvanted IIV3
- ccIIV4 refers specifically to cell-culture based IIV4
- HD-IIV3 refers specifically to high-dose IIV3
- SD-IIV3 and SD-IIV4 refer specifically to standard-dose IIVs