How the Flu Shot Works
In order to understand why someone would get the flu even though they got a flu shot, one must first understand how the flu shot works. The flu shot is determined every year by the World Health Organization (WHO). They determine which strains of the flu are most likely to occur in the population based on the flu virus that is present in the population. The Centers for Disease Control and Prevention (CDC) in the United States work with the WHO to determine which viruses will be most prevalent in our country. The virus selected is injected into eggs. (This is the reason someone with an egg allergy may wish to be monitored by a healthcare professional when receiving the flu shot.) Another virus is added to the virus. The two viruses develop inside the egg, until a vaccine is developed. The vaccine virus is then sent to manufacturers, who also have to test to determine if the strain will grow in eggs. The virus is then harvested out of the egg white. Parts of the pure virus are then killed, until only the antigen is remaining. An antigen is a receptor that connects to molecules in the body to produce immunity. The vaccine is then tested to determine if it will work. The entire process takes a minimum of five months to complete. Most flu vaccines are called "trivalent" vaccines, which means there are up to three viruses contained within each vaccine. Some flu vaccines may also be "quadrivalent" which means that the vaccine protects against up to four viruses.
Why You Still Got the Flu
Since flu vaccines are made so far in advance, determining which viruses to use in the vaccine are based on predictions, or best educated guesses. The vaccines are made of those viruses that are predicted will be most likely to be circulating in the coming year. However, since the flu virus is a living organism that has the ability to mutate or change, there is no guarantee that particular virus will be in the general population in the fall or that the virus itself will not have mutated thereby making the vaccine ineffective. When flu cases are rampant, one of two things may have occurred. An expected strain of the flu virus mutated or a new strain of flu virus appeared in the general population.
Why Get the Flu Shot
Depending on the year, the flu vaccine is between 30% and 80% effective. This year's flu vaccine is estimated to be about 36% effective. To put it into perspective, currently approximately 13,000 people in the United States die a year from complications from the flu, and another 200,000 this year have contracted the flu virus. In 1918, approximately 675,000 Americans died from complication from the flu that year. Approximately one third of the world's population at the time had contracted the flu virus. The first flu vaccines were used on U.S. military personnel in World War II. In 1957, another flu pandemic hit the United States, this time with approximately 116,000 deaths. In 1962, the Vaccination Assistance Act was passed allowing state and county health departments to receive government assistance to distribute the flu vaccine. In 1968, another flu pandemic hit the United States causing a loss of 100,000 lives. After this pandemic, scientists realized that the flu vaccine should be administered yearly and issued recommendations for those who should receive the flu shot. In 2009, another flu pandemic hit the United States. During that pandemic, 12,469 deaths resulted from complications of the flu. That is 1.8% of the number of people who died from the flu in the 1918 pandemic. Put another way, fewer people contract the flu today than died from the flu in 1918. This was largely due to the flu vaccine and other public health efforts during the past century. Getting the flu shot goes back to the concept of herd immunity. If one person gets the flu but ten others are vaccinated against it, the odds are then decreased that the other ten people will contract the flu from that one person.
Flu Prevention
There is no guarantee that someone will not get the flu during flu season. However, there are things individuals can do to make sure that they do so they will not contract the flu virus. Washing hands regularly, staying home when sick, covering the mouth with the forearm when coughing or sneezing, and wiping off possible infected surfaces regularly are all ways to limit the transmission of the flu virus.
Sources
“Influenza (Flu).” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 30 Oct. 2017, www.cdc.gov/flu/protect/keyfacts.htm.
“Influenza (Flu).” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 4 May 2016, www.cdc.gov/flu/about/season/vaccine-selection.htm.
“Pandemic Influenza Vaccine Manufacturing Process and Timeline.” WHO, World Health Organization, www.who.int/csr/disease/swineflu/notes/h1n1_vaccine_20090806/en/.
Commissioner, Office of the. “Press Announcements - Statement from FDA Commissioner Scott Gottlieb, M.D. on the Efficacy of the 2017-2018 Influenza Vaccine.” U S Food and Drug Administration Home Page, Office of the Commissioner, www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm597077.htm.
“Influenza (Flu).” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 2 Nov. 2017, www.cdc.gov/flu/pandemic-resources/basics/past-pandemics.html.
Mcneil, Donald G. “This Flu Season Is the Worst in Nearly a Decade.” The New York Times, The New York Times, 26 Jan. 2018, www.nytimes.com/2018/01/26/health/flu-rates-deaths.html.
Nesterova, Darya. "Information Sheet. Influenza Vaccination History." Vaccination Research Group. Virginia Tech. Oct. 2012. www.vaccination.english.vt.edu/wp-content/uploads/2015/04/updated-influenza-media-kit-4.pdf
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