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Can Influenza Cause Injury and/or Death?
The influenza virus is constantly mutating, and this frequent change makes it difficult to know exactly which type A and B strains will be circulating during the upcoming flu season. One particular strain of influenza may be predominant early in a flu season, while another different strain may emerge later in the season. Timing, severity and duration of the flu season varies widely from year to year, depending the prevalent circulating influenza strains that are associated with mild, moderate or severe illness.
Official estimates of annual influenza-associated deaths in the United States have varied widely during the last half century. In the past, the CDC has estimated between 3,000 and 49,000 influenza-related deaths occur every year in the U.S., but the actual number is unknown because influenza-related deaths for persons over age 18 are not required to be reported to the CDC. In recent years, the CDC has updated their numbers and now currently estimate that influenza-associated deaths between 2010 and 2020 average between a low of 12,000 and a high of 61,000. The CDC has also acknowledged that the actual number of persons in the U.S. who die every year from influenza-related complications is unknown.
A 2005 article published in the British Medical Journal asked the question: "Are U.S. Flu Death Figures More PR Than Science?" The author analyzed the U.S. Vital Statistics Mortality Data, which has been recorded for more than a century by the National Center for Health Statistics, and noted that from 1900 to 2010 the mortality rates for influenza deaths have been dropping and do not closely align with CDC influenza-related mortality estimates. Counting death certificates listing influenza as the cause of death could provide more accurate data; however CDC officials maintain this to be “a gross underestimation of seasonal influenza’s true impact.”
The impact of influenza-related illness on people also varies widely. A 2014 study published in The Lancet found that three-quarters of people confirmed with seasonal and pandemic influenza were asymptomatic, meaning they showed no symptoms of illness at all. People who do not show symptoms of influenza illness, whether they have been vaccinated or not, can still transmit infection to others.
For some people who get influenza, however, serious complications develop and can be life-threatening. These complications may include bacterial pneumonia, ear infections, sinus infections, dehydration, sepsis, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes.
IMPORTANT NOTE: NVIC encourages you to become fully informed about Influenza and the Influenza vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.
1 U.S. Centers for Disease Control and Prevention. Selecting Viruses for the Seasonal Influenza Vaccine. In: Influenza (Flu). Aug. 31, 2021.
2 U.S. Centers for Disease Control and Prevention. How the Flu Virus Can Change: “Drift” and “Shift”. In: Influenza (Flu). Oct. 15, 2019.
3 Biggerstaff M, Kniss K, Jernigan DB et al. Systematic Assessment of Multiple Routine and Near Real-Time Indicators to Classify the Severity of Influenza Seasons and Pandemics in the United States, 2003-2004 Through 2015-2016. Am J Epidemiol. May 1, 2018;187(5):1040-1050.
4 U.S. Centers for Disease Control and Prevention. Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976—2007. MMWR Aug. 27, 2010; 59(33):1057-1062.
6 U.S. Centers for Disease Control and Prevention. Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976—2007. MMWR Aug. 27, 2010; 59(33):1057-1062.
7 U.S. Centers for Disease Control and Prevention. How CDC Estimates the Burden of Seasonal Influenza in the U.S. In: Influenza (Flu). Nov. 22, 2019.
9 U.S. Centers for Disease Control and Prevention. Frequently Asked Questions about Estimated Flu Burden. In: Influenza (Flu). June 4, 2021.
11 National Vaccine Information Center. Influenza & Pneumonia Reported Deaths in U.S. 1940-2010 (Chart). No Date (Accessed Sept. 12, 2021).
12 U.S. Centers for Disease Control and Prevention. How CDC Estimates the Burden of Seasonal Influenza in the U.S. In: Influenza (Flu). Nov. 22, 2019.
13 Neel, J. How Many People Die From Flu Each Year? Depends How You Slice The Data. NPR Aug. 26, 2010.
14 Hayward AC, Fragaszy EB, Bermingham A. et al. Comparative community burden and severity of seasonal and pandemic influenza: results of the Flu Watch cohort study The Lancet Jun 2014;2(6):445-54.
15 The Lancet. Three-quarters of people with seasonal and pandemic flu have no symptoms AAAS Mar. 16, 2014.
16 Magalhaes I, Eriksson M, Linde C et al. Difference in immune response in vaccinated and unvaccinated Swedish individuals after the 2009 influenza pandemic. BMC Infect Dis. Jun 11, 2014;14:319.