Influenza is a concern for many reasons. Due to the severity of its symptoms, the high rates of transmission, the potential for secondary infections that may arise as a result of the immunological vulnerability that the virus creates, and the ever-changing nature of the virus, influenza remains a global threat (even with the creation of vaccines) (WHO, 2014). Influenza has caused four pandemics since the 1900, the most recent, a global outbreak of H1N1 occurring as recently as 2009 (WHO, 2018). The effects of influenza include disability and lost productivity due to illness, and even death (WHO, 2018). Before the 20th century, influenza pandemics, such as the outbreak of Spanish flu in 1918-1919, which was responsible for 20-50 million deaths worldwide (WHO, 2014). The development of vaccines to prevent against various seasonal and zoonotic strains of influenzas has greatly reduced of the number of people who get the disease, and the number of people who die from it (WHO, 2018). Influenza is classified as an airborne disease. The case definition of influenza is the operational definition that is needed in order to adequately surveil new cases of the disease and its progression within a population. The WHO currently defines a case of influenza as having “cough or sore throat, plus measured fever, shortness of breath and need for hospitalization” (Hirve et al, 2012). And while certain symptoms typify a case of influenza, such as “measured or reported fever,” plus “cough” and/or “sore throat,” Hirve et al, (2012) note that it is difficult to create an international case definition for influenza because cases are often dependent on the context or location of the outbreak. For example, a more tailored definition might also to include bodily pain, headache and malaise (Hirve, 2012). As such national/ and regional surveillance of influenza often different case definitions than the ones recommended by the WHO. People who are most at risk of influenza or complications from influenza include pregnant women, seniors, children under five, people with compromised immunity, pre-existing/chronic health conditions (e.g. diabetes, cancer, chronic respiratory illnesses, coronary heart disease, obesity, and smoking), healthcare workers, and Indigenous Canadians (WHO 2018; GOC 2017). Risk factors for zoonotic influenza include direct or indirect contact with an infected animal, living or dead, or being in animal-contaminated environments (WHO, 2018).In Canada, influenza is one of the top ten leading causes of death, resulting in an estimated 12 200 hospitalizations, and 3500 deaths per year (GOC, 2017). And according to the WHO (2008), the burden of disease for influenza in a developed country like the United States was 25–50 million cases per year, 150 000 hospitalizations, and up to 40 000 deaths. This accounts for between 10-20% of the population of developed countries being affected by the flu virus (WHO, 2008). When extrapolated, this equates to approximately 1 billion annual cases of influenza; and according to the WHO (2018), between 290 000 and 650 000 deaths a year globally, caused by seasonal forms of influenza (WHO, 2018). Incidence and prevalence for influenza can be difficult to measure, however data estimated using population-based surveillance data, such as hospitalization (Reed, et al, 2015). According the CDC (2018), the preliminary cumulative incidence in 13 US states, for the 2017-2018 flu season to date is 180 per 100 000 (see: Appendix A). In years when a certain strain is worse, or in a pandemic, the incidence will be high. Factors that contribute to increased incidence are better screening/reporting and surveillance. Epidemiology Importance and Study DesignA study by McIntyre et al (2014) was conducted on elderly people in London, Ontario to examine their perception and influences of getting seasonal influenza vaccine. As mentioned elderly adults are at risk for contracting the illness, therefore getting the influenza vaccine, which provides immunity against a specific yearly strain, is beneficial for this population. The researchers wanted to see what influenced their decision to get or not get the vaccine (McIntyre et al, 2014). A series of focus groups were conducted with a total of 37 vaccine using and non-using seniors, age 67-91 (McIntyre et al, 2014). The study found that beliefs about resilience and fear of vaccine side-effects were main influencers of vaccine non-use (McIntyre et al, 2014). This study is an example of a descriptive study design. As a cross-sectional analysis, it allows researchers to learn about people’s attitudes and practices within a population at a given time. It is a snapshot of what is going on at a particular time in a population, that might help formulate a hypothesis to be tested later on. Although cross-sectional analysis can be either descriptive or analytical, in this context, the data obtained was not used to compare the health outcomes of vaccine using versus non-vaccine using seniors. A second study from the literature was done by Gefenaite et al (2014). The authors conducted a test-negative case-control study in Lithuania, during the 2012-2013 influenza season, to assess the effectiveness of seasonal influenza vaccines against severe, lab-confirmed influenza in risk populations. Cases were hospitalized patients over age 18 with either the H1N1 and H3N1 strains of influenza A, or influenza B strain, and who self-reported that they had received or not received the seasonal influenza vaccine; controls were influenza-negative individuals (Gefenaite et al, 2014). Only patients who exhibited certain symptoms met the eligibility criteria for participation. The results showed that seasonal influenza vaccination did reduce the occurrence of lab-confirmed influenza (Gefenaite et al 2014). This is an example of an analytic study design because it attempts to test a hypothesis, and there is a measure the association between exposure (getting a seasonal influenza vaccine) and outcome (reduction of lab-confirmed influenza). However, this is not to say that correlation is causation. There may be additional factors that influence this observed outcome, such as small sample size or the imprecise nature of (retrospective) case-control design. Diseases can be described in terms of the three-dimensional interaction between agent, host and environment which influence the spread of disease, known as the “epidemiological triangle” (or triad). The goal of epidemiologists is to stop the disease from proliferating by breaking the triad at one of the following axes. At the top of the triad is the agent, the influenza virus itself. The influenza virus is indiscriminate, meaning anyone who is not immune can be a host (i.e. can potentially get the virus), however, some people are more susceptible than others (susceptible host). Animals can also be hosts of zoonotic influenzas. “Environment” is the third axes of the triangle. It involves external (situational, geographical, etc.) factors that facilitate disease transmission. According to Sooryanarain & Elankumaran (2015), influenza patterns are determined by temperature and humidity; the virus thrives in cool, dry conditions. This explains why seasonal influenza occurs in the winter months in temperate regions and is but severe, while the pattern in tropical regions is year-round but is mild (WHO 2008).The “chain of infection” describes the spread of influenza. First, the virus (agent) is transmitted to the reservoir or host. These can be either human or animal (in zoonotic influenza) (WHO, 2014). The “portal of exit” is the respiratory tract (nose, or mouth) via a sneeze, cough, talking, or runny nose. “Modes of transmission” are direct and indirect. Influenza is transmitted to a host directly when the mucus of an infected person directly contacts an uninfected person’s mucus membranes (ex. inhalation of the aerosolized secretions or droplets produced by the spit), or hand-to-mucosa transmission (WHO, 2014). Indirect contact involves touching a contaminated surface and then transferring the virus to your mucosa (WHO, 2014). “Portals of Entry” are mucus membranes (eye, nose, mouth) & the respiratory tract. Because seasonal influenza strains mutate, people must get vaccinated for new strains with each season. People who are not immunized against the latest strain are susceptible hosts (WHO, 2014).The disease progression of influenza viruses is relatively short. The virus typically only lasts between 2-7 days, during which time people will be symptomatic, but most people will recover in 7-10 days (GOC, 2017). The latent period of influenza can be short, and the incubation period can be between 1-4 days (usually 2 days) (GOC, 2017). The infectious period for adults (i.e. when they are capable of spreading the illness to others) is anywhere between the first day before flu symptoms begin until the fifth day after (GOC, 2017). Communicable Disease Prevention and Control Principles & Methods To prevent and control the spread of influenza, measures can be taken at each stage of the epidemiological triangle in order to break the chain. At the level of the agent, antiviral prophylaxis (drugs) can be taken by the host a viable method of disrupting the virus’s replication cycle, which will disrupt contagiousness and transferability (Spicknall et al, 2010). According to Bean, et al (1982), influenza A and B can survive on hard, non-porous surfaces for 24-48 hours, and on porous surfaces for up to 12 hours; therefore, proper cleaning and disinfecting of contaminated surfaces will either kill the virus or disrupt its survivability (Spicknall et al, 2010). Altering the host to stop the spread is also utilized. Protecting susceptible people through a combination of vaccination (one of the most effective methods of prevention and control), social distancing, school closure and restriction of public transport; and behaviour change such as hand washing, masks, and limited contact with infected persons will disrupt the chain at this level (Spicknall et al, 2010). Survival and transmissibility of influenza are greatly enhanced by cool, dry conditions rather than rainy ones (Sooryanarain & Elankumaran, 2015). Climate change, border closure, reducing population density, and vaccine promotion during peak influenza season in temperate zones could break the chain at the environmental level (Spicknall et al. 2010).Socio-political-economic-globalization Factors While it is important and necessary to discuss prevention and treatment, it is also important to look at the root causes or main issues that influence Influenza. A first such issue in modern-day international air travel. Globalization has created a global village in which it takes a relatively short amount of time to go around the world. With ease of transportation comes ease of transmission, which increases the likelihood of influenza reaching unimmunized populations, creating a pandemic. Rapid transmission is especially a problem when a particularly severe strain is brought into a population that has not been immunized against it. Related to the issue of rapid transmission is the second social issue related to modern influenza spread: urbanization and high population density. As seen in the 2009 outbreak of H1N1 in China, high contagiousness coupled with many people within close areas caused the disease to spread at an alarming rate (WHO, 2018). People who live heavily populated urban areas are at greater risk of coming in contact with an infected person and contracting influenza. As development occurs and more people move into cities this risk increases. Urban planning and equitable distribution of wealth are needed to mitigate this risk. A policy change that could be made to help limit the spread of influenza is to institute a national paid sick leave policy for employees. Public health (and common curtesy) recommends that people who are experiencing symptoms of influenza should stay home until they are well, to prevent the spread of the illness (GOC, 2017). However, for many individuals, staying home and losing a day’s pay is not feasible. The choice to work even with symptoms is not necessarily borne out of selfishness, but out of necessity; and the economic ramifications of missing work far outweighs the possibility of infecting others. Therefore, there an added financial incentive to stay home when sick might motivate their decision, and would be a benefit to employers as well, who would see fewer hours of work lost from entire workplaces contracting seasonal influenza.