Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can lead to death. The best way to prevent the flu is by getting a yearly flu vaccine. This essay will discuss in more depth the causes of influenza, symptoms, treatment options, prevention methods with a focus on vaccination, and the impact of this illness.
Influenza viruses are the cause of the flu. There are four types of influenza viruses (labeled A, B, C, and D) that spread to humans. Types A and B are responsible for seasonal flu epidemics each year, while type C causes a mild respiratory illness. Influenza A viruses are classified into subtypes based on two proteins on their surface called hemagglutinin (H) and neuraminidase (N). There are 18 different known HA subtypes and 11 known NA subtypes of influenza A viruses. Different combinations of HA and NA proteins create different subtypes. For example, the H1N1 and H3N2 subtypes are currently circulating in humans. Influenza B viruses are not divided into subtypes, but do divide into two antigenically distinct lineages known as B/Yamagata and B/Victoria. Influenza C and D cause mild disease in humans and are not thought to cause widespread epidemics. Influenza viruses constantly evolve through antigenic drift (gradual mutations) and occasional antigenic shift (major genetic changes). This makes developing immunity challenging and requires updates to influenza vaccines each year.
The symptoms of influenza can include fever or feeling feverish/chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, and fatigue. Some people may also experience vomiting and diarrhea, though this is more common in children than adults. Symptoms typically appear one to four days after being exposed to the virus and can last up to a week. Most people recover within a few days to less than two weeks, but some may develop complications (such as pneumonia) that require medical treatment or hospitalization. Complications are more common in young children, elderly people, and individuals with certain underlying health conditions.
If you suspect you have the flu, treatment should focus on relieving symptoms and managing pain with medication like acetaminophen or ibuprofen. Getting plenty of rest and drinking lots of fluids is also encouraged. Antiviral drugs like oseltamivir and zanamivir are another treatment option, though an influenza test would be needed for a diagnosis and to determine appropriate treatment. Antivirals work best when started within 48 hours of getting sick, though benefits may still occur when started later. Vaccination is the best way to prevent influenza infections, so antivirals would only treat symptoms after exposure rather than provide immunity. Antibiotics should generally not be prescribed, as they do not treat viral infections like the flu and inappropriately using antibiotics fuels antibiotic resistance.
Getting the flu vaccine is currently the best method for preventing influenza. The composition of seasonal flu vaccines is reviewed annually and updated to match the influenza viruses likely to circulate in the upcoming flu season. Most seasonal flu vaccines in the United States are either inactivated influenza virus vaccines (IIV) or recombinant influenza vaccines (RIV). IIVs are made from killed viruses and include trivalent seasonal flu vaccines and quadrivalent influenza vaccines. RIVs are made without influenza viruses and use genetic engineering technology. There are also live attenuated influenza vaccines (LAIVs) that contain weakened/modified live viruses and are administered intranasally. The flu shot is an inactivated vaccine that can be given to everyone 6 months and older, while the nasal spray LAIV is only approved currently for non-pregnant individuals 2-49 years old.
For the 2021-2022 flu season, flu vaccines protect against four different influenza viruses: an A/Victoria virus (H1N1), an A/Darwin virus (H3N2), and two influenza B viruses. It takes about two weeks for antibodies to develop in the body and provide protection against influenza virus infection after vaccination. While vaccination may not prevent all cases of flu, it has been shown in numerous studies to significantly reduce a person’s risk of illness, hospitalization, and even death. Vaccination also offers indirect protection to others by reducing the spread of disease. Vulnerable groups like pregnant women, young children, elderly adults, and those with certain health conditions are encouraged to get vaccinated to prevent serious complications from influenza.
In addition to vaccination, other actions can be taken to avoid contracting and spreading influenza viruses. Frequent hand washing, covering coughs and sneezes, disinfecting commonly touched surfaces, and avoiding ill individuals are important hygienic practices. Maintaining good health with sufficient sleep, a balanced diet, and exercise also support immune system function. During peak flu seasons, public health measures like school closures or event cancellations may be advised to limit social contacts that enable disease transmission. Wearing face masks in public has also been demonstrated to provide some additional protection against respiratory virus spread.
The impact of influenza is significant globally each year. According to the World Health Organization, seasonal influenza epidemics result in an estimated 1 billion cases, 3-5 million cases of severe illness, and 290,000-650,000 deaths worldwide annually. In the United States alone, the Centers for Disease Control and Prevention estimates that influenza has caused 9 to 45 million illnesses, 140,000-810,000 hospitalizations, and 12,000-52,000 deaths annually since 2010. Severe illness and deaths are not evenly distributed and predominantly affect high-risk groups. Young children, older adults aged 65 years and above, pregnant women, and those with chronic health conditions bear the heaviest burden of serious influenza disease. Beyond deaths, influenza also places a heavy economic burden on society through medical costs, lost earnings from missed work and school days, and long-term health consequences in some cases.
Influenza is a serious contagious disease that continues to have a major global health impact each year. Caused by influenza viruses, it can cause mild to severe illness with dangerous complications more commonly in at-risk groups. While treatment focuses on relieving symptoms, vaccination is the best way to prevent infection. By protecting communities through annual influenza vaccination programs and good hygiene practices, we can work to reduce influenza disease severity and spread. Ongoing influenza surveillance allows public health authorities to monitor viruses, update vaccines based on circulation patterns, and take necessary response actions. With coordinated global efforts, we can hope to curb the substantial health and economic consequences of seasonal and pandemic influenza.
Andrew Stroud