Inﬂuenza, commonly known as the ﬂu, is a contagious respiratory illness caused by inﬂuenza viruses that infect the nose, throat and lungs that can cause mild to severe illness. Serious outcomes of ﬂu infections can result in hospitalization or death.1 The best way to prevent the ﬂu is by getting vaccinated every year.
Most often present in the fall and winter months, the ﬂu can reach epidemic proportions in many geographic areas and communities. According to the CDC, each year between 3,000 and 49,000 Americans die from inﬂuenza-related complications, depending on the severity and length of each ﬂu season.2
Types of Influenza
Three types of inﬂuenza viruses infect humans: Inﬂuenza A, B and C. Type A and B cause seasonal epidemics. Inﬂuenza A is the only type known to cause pandemics and is further divided into subtypes, such as the H1N1 and H3N2 viruses. Inﬂuenza type C infections differ from Types A and B as they generally cause mild illness and are not thought to cause widespread ﬂu. Currently, the circulating inﬂuenza viruses are related to the pandemic 2009 H1N1 virus.
Each year, the seasonal inﬂuenza vaccine is designed to cover the three most common viruses expected to infect humans in the coming year. There are three kinds of ﬂu that are important to understand3:
- Seasonal ﬂu occurs each year, usually during late fall through early spring. Typically, between 5% and 20% of the U.S. population contract seasonal inﬂuenza, although only between 3% and 11% become symptomatic as seasonal ﬂu is so common and most have developed some natural immunity to these strains.
- Pandemic ﬂu is a speciﬁc kind of seasonal ﬂu that occurs when a new inﬂuenza A virus emerges for which most humans have little or no immunity and, thus, can spread efﬁciently and quickly. An inﬂuenza virus is called pandemic ﬂu when it rapidly spreads from person to person to create a worldwide epidemic (pandemic).
- Avian (H5N1) ﬂu is a subtype of the inﬂuenza A virus that is highly contagious among birds but rarely infects humans. Scientists follow H5N1 ﬂu closely because it has the potential to cause a deadly pandemic. So far, the majority of human H5N1 cases have occurred outside of the United States.4
Inﬂuenza is a yearly concern for health professionals as it is a constantly changing, highly infectious and potentially deadly virus.5
Contracting the Flu
The primary way that inﬂuenza viruses are transmitted is through droplet spread. When people infected with a ﬂu virus cough, sneeze or talk, they produce droplets that can land in the mouth, eyes or noses of people nearby. Less commonly, a person might also get the ﬂu through indirect contact: touching a contaminated surface or object and then touching their own mucous membranes (mouth, eyes or nose).6 Most healthy adults can infect others beginning one day before symptoms develop and up to ﬁve to seven days after becoming sick.7 Several groups are noted to have a high risk of transmitting inﬂuenza viruses, particularly school-age children7 (ages 5 to 19) and their parents.8 Healthcare workers, including ﬁre ﬁghters and other ﬁrst responders, also have signiﬁcant potential to transmit the virus through multiple patient contacts.
The ﬂu is different from the common cold. Symptoms of the ﬂu usually start suddenly and may include:
- Fever (not everyone with the ﬂu will have a fever)
- Feeling feverish or having chills
- Cough, sore throat and runny or stuffy nose
- Muscle or body aches
- Fatigue (tiredness)
- Vomiting or diarrhea9 (more common in children)
Although most healthy people recover from the ﬂu within one week, certain groups are at high risk for serious complications. Elderly people over 65, young children under 5, the immunocompromised, pregnant women and people with chronic conditions are more likely to become seriously ill and possibly die from inﬂuenza.10 Complications from the ﬂu include bacterial pneumonia, ear and sinus infections, and worsening of medical conditions such as congestive heart failure, asthma or diabetes.
The time from when a person is exposed and infected with ﬂu to when symptoms begin to show is about two days, but it can range from one to four days. A person may be able to spread the ﬂu to someone else before becoming symptomatic. People with the ﬂu are most contagious in the ﬁrst three to four days after illness onset and symptoms present.
Preventing the Flu
Inﬂuenza is a vaccine-preventable disease. The ﬂu vaccine has been shown to reduce ﬂu-related illnesses and the risk of serious complications. Ongoing research predicts the strains to be most common in the coming ﬂu season. One inﬂuenza A H1N1, one inﬂuenza B H3N and one or two Inﬂuenza B viruses are included in each season’s vaccines. About two weeks after vaccination, antibodies that provide protection against inﬂuenza virus infection develop in the body. The CDC and the Advisory Committee on Immunization Practices (ACIP) do not recommend one vaccine form over others.
An annual inﬂuenza vaccine is recommended for all ﬁre ﬁghters in NFPA 1582, Fire Department Infection Control Programs. Emergency responders need to be vaccinated with the seasonal ﬂu vaccine every year. Currently, there are two kinds of ﬂu vaccine available in the United States11:
- The ﬂu shot — an inactivated vaccine (containing killed virus) is approved for use in people older than 6 months, including healthy people and people with high-risk, chronic medical conditions
- The nasal-spray ﬂu vaccine — a live vaccine (containing weakened viruses) that does not cause the ﬂu (sometimes called LAIV for live attenuated inﬂuenza vaccine or FluMist®). Nasal vaccines are approved for use in healthy, non-pregnant people who are 2 to 49 years of age
Neither vaccine will cause a person to contract the virus; however, some individuals may experience mild ﬂu-like symptoms from the body’s immune response.12 The ﬂu vaccine effectiveness varies year to year, but can reduce the risk of having to go to the doctor because of the ﬂu by 40-60%.13 It is important to note that seasonal ﬂu vaccines do not protect against infection or illness caused by other viruses, such as COVID-19, that can also cause ﬂu-like symptoms. There are many other viruses besides inﬂuenza A or B that can result in inﬂuenza-like illness that spread during ﬂu season.
In addition to vaccination, you can help prevent the spread of inﬂuenza by:
- Staying home from work and school if you are experiencing ﬂu-like symptoms
- Practicing decontamination procedures will protect you, your crew and your family from indirect contact. Viruses and bacteria can live for up to two hours or longer on surfaces such as radios, doorknobs and equipment.13
- Socially distancing from patients with respiratory symptoms
- Strictly limiting the number of crew members having direct patient contact
- Practicing hand hygiene (wash with soap and water or use hand sanitizer with at least 60% alcohol)
- Use personal protective equipment (PPE) (gloves, gowns, NIOSH-certiﬁed respirators that are N95 or higher and goggles that offer mouth, nose and eye protection)14,15
- Providing masks for symptomatic patients
If You Believe You Have Inﬂuenza16
- Stay home from work or school when you are sick
- Contact your healthcare provider to discuss possible testing and treatment.
- Because many respiratory illnesses — such as the common cold and COVID-19 — have symptoms similar to the ﬂu, it can be difﬁcult to diagnose inﬂuenza. If you develop ﬂu-like symptoms and are concerned about your illness, especially if you are at high risk for complications of the ﬂu, it is important to contact your healthcare provider.
- Tests to diagnose inﬂuenza are most effective if performed within the ﬁrst two or three days of illness.
- Antiviral treatments for inﬂuenza work best when started within two days of symptom onset. While most people do not require medication, antiviral therapy can be very important in certain situations (e.g., hospitalized patients, high-risk groups, severe complications).17
8Medlock J, Galvani AP. Science. “Optimizing influenza vaccine distribution”2009 Sep 25;325(5948):1705-8. Epub 2009 Aug 20