Influenza has been impacting public health on a global scale since the beginning of recorded history. Influenza, also known as the “flu,” has numerous organizations committed to public health research, developing vaccines, and educating on best practices to prepare for the upcoming flu season. By gaining an understanding of the flu through history, virology, and how it impacts our society, we can have a better appreciation for the commitment that’s involved with combating the flu.
What Is Influenza (and What’s Not)?
The eyes of an epidemiologist can twitch for a variety of reasons, one of them being when someone says they have the “stomach flu.” In reality, influenza is an acute respiratory disease caused by the influenza virus. Symptoms usually include fever, a non-productive cough, headache, sore throat, muscle aches, and fatigue.1
The “stomach flu” is most likely gastroenteritis, commonly caused by the norovirus; a virus which causes symptoms such as cramping, nausea, vomiting, and diarrhea and is also highly contagious.1 The U.S. sees about 20 million norovirus-related illnesses each year.2
Alternatively, another similar ailment during flu season is the garden-variety common cold. Although both the flu and cold are respiratory illnesses, the flu usually has more severe and sudden onset of symptoms while the common cold usually includes a gradual onset of symptoms such as sneezing, head congestion and a sore throat. Self-diagnosing these illnesses incorrectly can lead to ineffective at-home treatment or even a delay in seeking medical attention when it’s warranted.
Seasonal Flu & Virology
Influenza cases occur year-round, but the U.S. experiences a seasonal flu spike during the fall and winter months, often peaking between December and February each year. There have been a lot of hypotheses as to why flu epidemics occur in winter months, such as people spending more time indoors with others or lack of vitamin D from sunlight compromises the immune system.
A study in 2007 found that the flu virus spreads and survives better in cooler, dry climates within the northern hemisphere. Because influenza is a respiratory virus, it’s spread through the air in tiny droplets. When temperatures and humidity are low, droplets travel further and longer compared to higher temperatures and humidity, where the droplets grow bigger from surrounding water in the air and fall faster away from passersby.3
On the other hand, tropical southern hemisphere climates experience flu epidemics during the rainy season, which appears contradictory to colder climate epidemic timings, but there’s little data to explain the reasoning.
One of the most important distinctions to understand about the flu is the difference between an epidemic and a pandemic. We experience a flu epidemic every flu season throughout our communities. In contrast, a pandemic of influenza is rare and occurs when two criteria are met: 1) There’s a new Influenza A virus that’s able to infect people; and 2) That this new virus has spread beyond one geographical location to a global level.
Every season we’re told which type of flu strain is circulating this year, but how many different strains of flu are out there? For perspective, the 2017–2018 season was primarily Influenza A (H3N2) and in 2009, our country experienced an H1N1 pandemic, also known as the “swine flu,” because it originated in pigs.
There are three main types of influenza that afflict humans: Influenza A, B and C. For example, H1N1 is a subtype within Influenza A, and there are potentially 144 different subtypes.4 We hear more commonly about the subtypes in the news such as H1N1, H3N2, etc. These differences are identified by the types of protein located on the virus: hemagglutinin (H) and neuraminidase (N). Within a subtype, there are also several variants due to the hemagglutinin gene constantly mutating. Because of these mutations, it can be difficult to predict exactly which flu strain will strike every year and requires an educated guess.
The earliest recordings of symptoms similar to the flu have been found in Greek culture dating back to 412 BC.5 One of the more deadly pandemics of modern recorded history was the “Spanish flu” outbreak of 1918. This pandemic—determined to be attributed to the H1N1 strain—lasted from 1918–1920, infecting over 500 million people, approximately one-third of the world’s population.5,6 It was unique in that it had such a high mortality rate amongst healthy individuals, where the flu usually affects young children and the elderly.6 By the end of the ordeal, the pandemic caused the deaths of at least 50 million people.5
The most recent influenza pandemic occurred in 2009, also caused by a strain of H1N1.5 This outbreak originated in Mexico and was originally termed the “swine flu.” Initially, the death toll from this pandemic was at 18,500 confirmed cases, but it’s estimated to have caused up to 575,000 deaths with 80% of deaths occurring in individuals under the age of 65. Of these deaths, approximately 51% occurred in Asia and Africa.7
In recent years, the flu vaccine has received a bad reputation for low rates of effectiveness. With all of the technology we have access to, it’s been asked, “why can’t we do better at producing an effective vaccine?”
Studies have shown the flu vaccine reduces the risk of infection by 40–60% if the vaccine produced is a match to the flu virus in current circulation.8 One of the major problems is when the vaccine isn’t a match for the predominantly spreading virus, and vaccine protection rates can drastically decline. Another factor is how an individual responds to the flu vaccine, as a recent study found that poor immune responses may play a large role in low effectiveness.9
As an epidemiologist, I often hear feedback about influenza and vaccines. One comment I commonly hear is, “well, it’s not effective this year, so I’m not going to bother getting the vaccine.” Unfortunately, the news doesn’t focus on the number of people estimated to have benefited from the influenza vaccine. Although it’s too early to obtain conclusive numbers for last season, the 2016–2017 influenza vaccine is estimated to have prevented 5.29 million illnesses, 2.64 million medical visits, and 84,700 hospitalizations. According to the CDC, if vaccination rates increased by 5%, an additional 483,000 illnesses could have been prevented.10
Photo courtesy Centers for Disease Control and Prevention
Another misconception is when individuals tell me, “I got the flu from the vaccine, so I’m not going to get it anymore.” This is a major myth and goes back to the saying “correlation vs. causation.” If the individual did actually get the flu, it was simply poor timing and not caused by the vaccine. Individuals can experience side effects such as fever, headache and muscle aches that might lead one to believe they have the flu. Although choosing to receive the flu vaccine is a personal choice, it’s important to remember that the vaccine not only provides protection to the individual receiving it, but also those in contact with that individual throughout the flu season, and it ultimately creates an unseen ripple effect.
Economic Burden of the Flu
The illness is undoubtedly a burden on the flu-stricken individual, not only feeling ill for several days, but also having to put their life on hold by missing work, school and other activities. The flu also puts a strain on the U.S. economy every year. A 2018 study looked at the 2015 flu season and estimated the total economic burden was $11.2 billion that included: ill, but not medically attended individuals; outpatient visits; ED visits; hospitalizations; deaths and lost days of productivity.11
Beyond the burden of lost school and work days, a community experiencing an outbreak can lead to reduced social contact such as visiting restaurants, shopping, or attending large public events. Overall, it’s a daunting task to calculate all costs associated with influenza because only a portion of individuals are actually tested for the influenza virus, therefore, the total number afflicted remains speculative. As with any infectious disease, there’s a ripple effect, where one infected individual can infect three other individuals, and those individuals will infect three more, and so on. This not only affects the individuals, but also the economic system they belong to.
Importance of Surveillance
Public health stakeholders recognize the potential operational advantages for agencies around the country to be as prepared for the flu season as much as possible. Through continued scientific research and the application of epidemiological practices, flu vaccines will improve and communities will have the opportunity to be more aptly prepared for the flu season.
There are limited resources within any community such as staffing, equipment and finances. When those resources are at full capacity and ultimately strained, decisions regarding priority need to be made. When resources require allocation towards a specific community problem, such as a flu outbreak, resources are pulled away from other areas. This is why it’s important to plan ahead, in preparation of a possible outbreak based on past data and lessons learned at a community level on how to best approach each flu season.
The pre-existing data within the EMS and hospital setting can provide a retrospective look at how past flu seasons have affected a community and its resources. Working with an epidemiologist can help an organization discover insights and trends related to the flu and will allow a community to prepare on multiple levels for future flu outbreaks.
1. Budd A, Blanton L, Grohskopf L, et al. (Nov. 10, 2017.) Manual for the surveillance of vaccine-preventable diseases. Chapter 6: Influenza. Centers for Disease Control and Prevention. Retrieved Sept. 18, 2018, from www.cdc.gov/vaccines/pubs/surv-manual/chpt06-influenza.html.
2. Centers for Disease Control and Prevention. (Sept. 11, 2018.) Prevent the spread of norovirus. Retrieved Sept. 18, 2018, from www.cdc.gov/features/norovirus/.
3. Lowen A, Mubareka S, Steel J, et al. Influenza virus transmission is dependent on relative humidity and temperature. PLoS Pathog. 2007;3(10):e151.
4. Centers for Disease Control and Prevention. (Sept. 27, 2017.) Types of influenza viruses. Retrieved Sept. 18, 2018, from www.cdc.gov/flu/about/viruses/types.htm.
5. Potter C. A history of influenza. J of Applied Microbiology. 2001;91(4):572–579.
6. Centers for Disease Control and Prevention (March 21, 2018.) History of 1918 flu pandemic. Retrieved Sept. 28, 2018, from www.cdc.gov/flu/pandemic-resources/1918-commemoration/1918-pandemic-history.htm.
7. Dawood FS, Iuliano AD, Reed C, et al. Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: A modelling study. Lancet Infect Dis. 2012;12(9):687–695.
8. Centers for Disease Control and Prevention. (Sept. 6, 2018.) Vaccine effectiveness—How well does the flu vaccine work? Retrieved Sept. 18, 2018 from www.cdc.gov/flu/about/qa/vaccineeffect.htm.
9. Wood M. (Feb. 20, 2018.) Why doesn’t the flu vaccine work sometimes. University of Chicago Medicine. Retrieved Sept. 18, 2018, from www.uchicagomedicine.org/biological-sciences-articles/why-doesnt-the-flu-vaccine-work-sometimes.
10. Centers for Disease Control and Prevention. (May 22, 2018.) Estimated influenza illnesses, medical visits, and hospitalizations averted by vaccination in the United States. Retrieved Sept. 18, 2018 from www.cdc.gov/flu/about/disease/2016-17.htm .
11. Putri W, Muscatello D, Stockwell M, et al. Economic burden of seasonal influenza in the United States. Vaccine. 2018;36(27):3960–3966.