Last updated date: 10-Apr-2023

    Medically Reviewed By

    Medically reviewed by

    Dr. Btissam Fatih

    Medically reviewed by

    Dr. Kim Irina

    Originally Written in English

    Symptoms of Flu

      Symptoms of Flu


      What is Flu?

      Flu, also known as influenza, is an infectious respiratory condition. It occurs due to viruses that affect the throat, nose, and even the lungs. Although it can sometimes be mistaken for cold, the flu is relatively different. Besides, the symptom of flu can vary slightly from those of cold and can last for an extended period. 

      Flu can subside or heal on its own in some people. But in other cases, it can result in life-threatening complications. Everyone is at risk of developing the condition. Hence, the best method of preventing it is through annual flu vaccination. 

      Most healthy people recover completely within a few days of infection, although complications such as pneumonia and mortality occur in some high-risk populations. Young children, the elderly, the immunocompromised, and pregnant women are among these categories.

      A runny nose, high fever, cough, and sore throat are all symptoms of influenza. Seasonal outbreaks of influenza spread quickly and efficiently. Flu epidemics occur every fall and winter in temperate countries, affecting a considerable number of adults and children, although the season’s influence age groups and severity differently. 



      In 1933, researchers identified Influenza A; seven years later, they isolated Influenza B. The presence of influenza viruses in certain geographic locations of the northern and southern hemispheres is referred to as an influenza epidemic, which happens every year during the winter months. The intensity, duration, and age groups most affected by influenza, as well as complication rates such as hospitalizations and fatalities, vary significantly across influenza seasons.

      When H3N2 viruses prevail, the season is more severe, particularly among youngsters and the elderly. The World Health Organization (WHO) undertakes worldwide influenza virologic monitoring, which demonstrates that influenza viruses are isolated from individuals in a geographic region every month. During the winter months, influenza activity in temperate regions increases.

      In the Northern Hemisphere, influenza outbreaks and epidemics normally occur between October and March, whereas influenza activity occurs between April and August in the Southern Hemisphere. In the tropical belt, influenza is present all year.


      Causes and Triggers of Flu

      If anyone with influenza sneezes coughs or speaks, the virus spreads across the air in droplets. Thus, you can directly inhale the droplets or pick up the infections from an object, including a computer keyboard or phone. You will then move them towards the nose, eyes, and mouth. 

      Individuals infected with the virus are mostly infectious right from the day before the symptoms emerge five days after they appear. Minors and people with compromised immune systems can remain infectious for an extended period. 

      The flu viruses are still evolving, with new strains emerging on a regular basis. If you have once ever had influenza, then the body has already produced antibodies to combat the strain of the virus. So, if future flu viruses are the same as those you have already experienced, either through infection or vaccination, the antibodies can help prevent or limit the severity of the condition. However, the level of antibodies can drop with time. 

      Furthermore, the antibodies to flu viruses that you have previously had do not safeguard against new influenza strains. This is because they may be different from the viruses you have encountered before. 


      Risk Factors of Flu  

      Some of the factors that are likely to increase the chances of developing influenza or aggravate the symptoms of flu include; 

      • Age: Usually, seasonal flu mostly affects children aged between six months to five years old. Also, adults aged 65 and above are at high risk. 
      • Working and living conditions: Most individuals residing or working in places where there are a lot of people have increased chances of getting the flu. Such sites include military barracks and nursing homes. In addition, people who are in the hospital are even more vulnerable to infection. 
      • A compromised body immune system: A person’s immune system can be weakened by cancer medications, anti-rejection drugs, prolonged use of steroids, blood cancer, organ donation, and HIV/AIDS. This makes it relatively easier to catch the flu, as well as increases the chances of various complications. 
      • Race: According to various studies, Native Americans might be at a higher risk of developing flu complications.
      • Chronic health conditions: At times, certain chronic medical conditions can increase the likelihood of flu complications. Examples of these disorders are lung problems like asthma, heart disease, diabetes, nervous system diseases, airway abnormality, metabolic disorders, and liver, kidney, or blood disease. 
      • Obesity: Flu risks and complications are more likely in individuals with a body mass index (BMI) of 40 or higher. 
      • Using aspirin while below 19 years: If infected with flu, people under the age of 19 who are on long-term aspirin treatment have increased risks of having Reye's syndrome. 
      • Pregnancy: Flu complications are more common in pregnant women, especially during the second to third trimesters. Up to about two weeks after giving birth, women are still at risk of developing flu-related complications. 



      Influenza is an acute respiratory illness that causes inflammation of the upper respiratory tract and trachea. The acute symptoms last seven to 10 days, and the sickness is self-limiting in the majority of healthy people.

      The viral syndrome, which includes high fever, coryza, and bodily pains, is caused by the immunological response to the viral infection and the interferon response. High-risk populations, such as those with chronic lung illness, heart disease, or pregnancy, are more likely to have serious consequences such as primary viral pneumonia, subsequent bacterial pneumonia, hemorrhagic bronchitis, and death.

      These serious consequences might arise as soon as 48 hours after the onset of symptoms. Starting at the moment of injection, the virus replicates in the upper and lower respiratory airways, peaking after 48 hours on average.

      Both neuraminidase and hemagglutinin are essential for virulence since they are the primary targets of neutralizing antibodies. Hemagglutinin binds to epithelial cells in the respiratory system, allowing the infection to spread. Neuraminidase breaks the connection that binds the virus together, allowing the infection to propagate. Their H and N proteins are responsible for identifying influenza viruses.

      A critical component of the influenza A virus is a genetically labile virus with a high mutation rate. This causes significant alterations in antigenic and functional proteins.


      Types of Flu Viruses 

      Humans are normally infected with three types of flu viruses, including type A, type B, and type C. there is also another fourth kind, type D, but it does not affect humans. 

      During the epidemic season, influenza types A and B infect humans. Influenza A is classified into numerous subtypes based on the mix of hemagglutinin (H) and neuraminidase (N) proteins produced on the virus's surface.

      Since the flu virus can be transferred from animals to humans, humans and animals can catch type Flu. This virus is continually evolving and has the potential to trigger annual flu epidemics. As such, the symptoms of flu-type A also vary. 

      Over the winter season, Type B flu can result in seasonal outbreaks. On the other hand, this form is usually less severe, unlike type A and involves fewer mild symptoms. The symptoms of flu-type B can sometimes lead to serious complications. Besides, type B can only be passed from one individual to another. 

      Type A and B flu are associated with different strains. On the other hand, humans and certain animals are affected by Type C flu. But it has minor side effects and few risks.

      If the antigenic properties of the virus alter, animal influenza viruses can cause illnesses in people. Transmission from person to person is frequently ineffective when this occurs. Influenza pandemics, such as those that occurred in 1918 and 2009, are possible if the transmission from person to person becomes efficient.

      Avian influenza, sometimes known as bird flu, is an infectious illness of birds caused by influenza A viruses such as A(H5N1), A(H5N8), and H7N9. These viruses are concerning because they have the potential to evolve and become transmissible from person to person, resulting in a severe pandemic.

      The 2009 pandemic influenza, which is an animal influenza virus that likely began in South America in early 2009 and evolved the potential to transmit from person to person and internationally, is an excellent example of animal origin influenza. 


      Symptoms of the flu

      The flu can appear to be a common cold at first, with a runny nose, a sore throat, and sneezing. On the other hand, Colds normally take some time to develop, while the flu strikes unexpectedly. While a cold can be annoying and irritating, the flu normally makes you feel even worse. 

      The following are some of the most common signs and symptoms of the flu virus; 

      • Fever 
      • Chills and sweating 
      • Sore throat
      • Aching muscles 
      • Constant dry cough 
      • Headache 
      • Weakness, tiredness, or fatigue 
      • Shortness of breath 
      • Stuffy or running nose 
      • Diarrhea and vomiting (especially in children)
      • Eye pain


      Symptoms of flu in kids

      The flu is one of the most serious and widespread viral infections throughout the winter season. The majority of youngsters are sick with the flu for less than a week. However, some children have more serious illnesses and may require hospitalization. The flu can potentially cause a lung infection (pneumonia) or even death.

      The flu is a respiratory disease, but it may affect the entire body. A kid can become unexpectedly ill with any or all of the following symptoms:

      • Fever, which may be as high as 103°F (39.4°C) to 105°F (40.5°C)
      • Body aches, which may be severe
      • Headache
      • Sore throat
      • Cough that gets worse
      • Tiredness
      • Runny or stuffy nose

      In some cases, your child may also have symptoms such as:

      • Nausea
      • Vomiting
      • Diarrhea

      The flu usually clears up in a week for most youngsters. However, kids may continue to feel fatigued for up to 3 to 4 weeks.


      Flu Contagiousness 

      The flu virus spreads through liquid droplets. When a person coughs, sneezes breathes, or talks, they may spread the virus to another person up to 6 feet away. 

      A virus may be passed on by a healthy person a day before they develop symptoms. This also means that you are likely to spread the flu before you even realize you have it. After symptoms emerge, an infected person may continue to spread the virus for up to five or seven days. 

      Individuals with a weak or compromised immune system, including the elderly and small children, may spread the virus for longer. During the first three to four days after symptoms occur, flu tends to be more infectious. 


      Flu Transmission and Incubation 

      If virus-containing droplets from another person's breath get into a person's mouth, nose, or lungs, they may develop flu symptoms. Such a transmission is possible due to reasons such as; 

      • Someone who does not have the virus is in close proximity to someone who has the flu.
      • A virus-free person touches an item touched by someone infected with the virus and then touches their mouth, eyes, or nose.

      The time between when a virus infects a person and when symptoms appear is known as the incubation period of an illness. This usually takes about two days for flu, but it can last anywhere from one to four days. Even before symptoms occur, a person may spread the virus.

      Symptoms of the flu occur unexpectedly, often two days following infection. The majority of symptoms go away after about a week, although a cough can last up to two weeks. An individual can remain infectious for up to a week, even after the symptoms have gone away in certain cases.

      Complications may take longer to subside if they arise. Some of the most serious complications, such as kidney failure, may have a long-term effect on the health of a person. 

      After the major signs and symptoms resolve, some individuals experience post-viral exhaustion for about a week or more. Also, they might have a residual feeling of tiredness and malaise. 


      Flu Diagnosis 

      Clinical diagnosis of influenza is possible, especially during the influenza season. The majority of instances will heal without medical care, and they will not require a laboratory test to be diagnosed.

      If you suspect a flu infection, the doctor can start by performing a physical examination. This is to check for signs and symptoms of flu. If necessary, they can potentially request an influenza virus test. 

      You might not necessarily require to undergo influenza tests at periods when the virus is widespread. In such cases, the doctor can make a diagnosis according to the evident symptoms and signs. 

      Rapid antigen detection, a rapid molecular assay for viral RNA detection, immunofluorescence direct and indirect antibody staining for viral antigen detection, real-time PCR testing, and cell culture are all accessible laboratory procedures for the diagnosis of influenza.

      All rapid tests have limited sensitivity and a significant false-positive rate. In individuals with pulmonary symptoms, a chest x-ray should be taken to rule out bacterial pneumonia.

      In most hospitals and laboratories, polymerase chain reaction (PCR) examination is becoming more popular. This test can be performed when you are in the hospital or at the doctor's office. PCR testing is more reliable than other tests and capable of distinguishing the strain of influenza. 

      With the COVID-19 pandemic, a test to detect influenza, as well as COVID-19, is accessible. COVID-19 and influenza may both be present at the same time. 


      Flu Treatment 

      In most healthy people with no additional comorbidities, influenza infection is self-limiting and mild. In healthy people, no antiviral medication is required for mild infections.

      The flu is usually treated with rest and plenty of fluids. The doctor can recommend an antiviral medication to cure the flu if you have a serious infection or are at risk of severe complications. Oseltamivir (Tamiflu), peramivir (Rapivab), zanamivir (Relenza), and baloxavir (Xofluza) are examples of these drugs. These medications can help you recover faster by reducing the length of your illness by a day or two. With this, you can avoid serious complications. 

      Oseltamivir is an orally administered drug. On the other hand, Zanamivir is inhaled using an appliance that looks like an asthma inhaler. It’s, however, not recommended for people who have serious respiratory conditions like asthma or lung disease. 

      During recent influenza seasons, considerable rates of resistance to adamantanes antivirals have been observed in influenza A, and they are not indicated for therapy or prevention against influenza A. Resistance to neuraminidase inhibitors has been minimal in recent influenza seasons, but the virus might evolve and gain resistance at any time.

      Following therapy, certain individuals, particularly immunocompromised ones, may develop resistance. In cases of outbreaks and exposure in high-risk populations, oseltamivir can be used for chemoprophylaxis in persons aged one year and older.

      Oseltamivir side effects include severe skin responses and occasional temporary neuropsychiatric episodes; these side effects make oseltamivir unsuitable for usage in the elderly and persons who are predisposed to developing these adverse effects. An allergy to eggs is the only contraindication of zanamivir. 


      How to Prevent Flu?

      How to Prevent Flu?

      Due to the risk of complications, it's essential to protect yourself as well as your family against the virus. The flu virus can be passed from one person to another. Hence, you should clean your hands regularly using soap or an alcohol-based hand sanitizer to avoid contacting it. Also, try to avoid rubbing your nose or mouth with your hands, especially if you have not washed them.

      The flu virus is capable of surviving for up to 48 hours on hard surfaces and items. To further protect yourself, you should use disinfectant wipes and spray on the most touched surfaces around the house or work. 

      Wear a face mask to guard yourself while you're caring for a person with the flu. Covering the cough and sneezes will help prevent the flu from spreading. Medical providers often recommend coughing or sneezing into the elbow rather than hands. 

      Try to get a vaccination against the flu at least once a year. Every person or child above the age of six months should get the vaccine. It guards against the flu virus's most common strains. Despite the fact that the vaccine is not 100 percent efficient, it can help minimize flu risk by approximately 40 to 60%. This is based on the CDC sources. 

      Doctors normally administer the influenza vaccination through injection on the arm. The nasal spray flu vaccine is suitable for people aged between 2 to 49 years and women who are not pregnant. 

      Vaccination is strongly advised at the start of the winter season. Among the flu vaccination recommendations are:

      • Individuals aged six months and up
      • Individuals who have an egg allergy but only suffer hives should get the immunization.
      • In all situations, resuscitation equipment must be present, and the patient must be followed for 10-15 minutes.
      • In past years, the nasal flu vaccination was ineffective. The injectable method is favored.
      • Pregnant women can receive the flu vaccination.
      • Vaccination is frequently ineffective in those over the age of 65, hence high-dose formulations should be utilized.


      Flu Shot 

      Getting an annual flu vaccination is the best method of preventing the infection. Typically, there are two forms of flu vaccination; flu shot and nasal spray flu vaccine. 

      The doctor usually gives the flu shot using a needle, mostly in the arm. It's safe for everyone over the age of six months as well as healthy individuals and those with serious illnesses. On the other hand, the nasal-spray flu vaccine contains live and weak influenza viruses that do not trigger conditions. 


      Seasonal Flu Shot

      Based on the centers for disease control and prevention (CDC), a flu shot comprises a vaccine for a range of viruses. They include the influenza A (H1N1) virus, influenza virus (H3N2), and one or two influenza B viruses. 

      Viruses, on the other hand, evolve and transform with time. As a result, medical scientists might have to change the content of vaccines every year. Experts use statistics from international monitoring programs to forecast the flu strains that will be prevalent during a certain flu season. Approximately two weeks following administration of the vaccine, protection starts. For instance, seasonal influenza vaccination can begin in September or earlier once the vaccine is all set. After that, it can continue all the way during the flu period till January or beyond. 


      Flu Symptoms Remedies 

      Having a flu infection can be irritating as the associated symptoms cause a lot of discomfort. However, there are flu symptoms treatments and remedies available, and most of them offer significant relief. 

      Therefore, if you have the flu, keep the following remedies in mind; 

      • Cough suppressants medication: Coughing is a typical flu symptom that doctors recommend using some drugs to relieve. Alternatively, if you are not comfortable with taking medicine, certain cough drops contain honey and lemon. This can help relieve a sore throat as well as a cough. 
      • Decongestants: This form of the drug can help alleviate nasal congestion as well as sinus and ear pressure. Every form of decongestant has its own set of side effects. Therefore, it's essential to read the labels carefully to find the right for you. 
      • Expectorants: This form of drug aids in loosening thick sinus secretions that clog the head and trigger coughing.
      • Pain relievers: Doctors often recommend analgesics such as acetaminophen and ibuprofen to alleviate flu symptoms in babies and adults. Muscle aches and pains, fever, and headaches are examples of such symptoms. 


      Flu Shot for Children 

      Flu Shot for Children

      Hundreds of thousands of minors contact the flu every year. Some of these ailments are chronic and necessitate hospitalization. Without treatment, others can even lead to death. 

      When it comes to the flu, children are always at greater risk, unlike adults. Mostly, children under the age of five are more likely to require immediate medical treatment for influenza. 

      Children below the age of two are at the highest risk of severe influenza complications. The flu could be worse for your child if he or she has a chronic health condition such as asthma and diabetes. In case your child gets exposed to the flu or is exhibiting flu symptoms, consult a physician right away. You should also call ahead to get the COVID-19 preventive protocol.

      A flu vaccine is the safest way to protect children from the flu. Annual vaccination is thus essential. On the other hand, medical providers recommend vaccination for anyone above six months old.  


      Flu Shot and Pregnancy 

      Getting the flu shot while pregnant is both healthy and safe; hence doctors often recommend it. It can take around two weeks for the defense to take effect and ease the symptoms of flu when pregnant. The flu vaccine would also go through to the fetus, providing some protection against the infection. 

      A flu vaccine is not recommended for newborns since it can be harmful to them. However, both the mother and the unborn baby will benefit from the vaccine. 


      Symptoms of Flu vs Cold

      At first glimpse, the flu and common cold may appear to be the same thing. They are both respiratory diseases with associated symptoms that are alike. These two disorders, however, are caused by different viruses. One can notice the difference between them depending on the symptoms. 

      There are some common symptoms of flu vs. cold. Most people who suffer from either disease usually experience the following symptoms; 

      • Sneezing 
      • Stuffy or running nose 
      • General body weakness 
      • Body aches 

      Flu symptoms are usually more intense than cold symptoms. Another significant distinction between the two is their seriousness. Colds seldom lead to other illnesses or problems. However, the flu can cause ear infections, sinusitis, sepsis, and pneumonia. 

      If the symptoms are serious, you should seek medical advice to determine whether you have a cold or the flu. In most cases, the medical provider will conduct a few tests to assess the cause of the symptoms. 

      For the COVID-19 outbreak, call ahead to find out if you can see a doctor in person or schedule an online appointment. Since cold and flu symptoms in toddlers, children, and adults coincide with COVID-19 symptoms, they should be addressed cautiously.

      If the doctor detects a cough, you will just need to take care of the symptoms until the infection resolves. The following are examples of treatments; 

      • Taking cold medicines that are available over-the-counter (OTC)
      • Maintaining hydration
      • Having enough sleep

      Taking flu medication early during the virus's cycle can help minimize the seriousness of the disease and the duration of sickness. For those who have the flu, rest as well as hydration are also helpful. The flu, like the common cold, will take a long time to pass through the body.


      Differential Diagnosis

      • Acute Respiratory Distress Syndrome (ARDS)
      • Adenovirus
      • Arenaviruses
      • Cytomegalovirus
      • Dengue
      • Echovirus infection
      • Hantavirus pulmonary syndrome
      • HIV infections
      • Legionnaires disease
      • Human Parainfluenza Virus (HPV)


      Flu Complications 

      The flu is typically not serious if you are younger and healthy. While you can feel awful when you have the flu, it normally resolves in one or two weeks with no long-term consequences. However, high-risk children and adults are likely to experience complications such as; 

      • Bronchitis 
      • Pneumonia 
      • Heart disorders 
      • Asthma flare-ups 
      • Acute respiratory distress syndrome 
      • Ear infections

      In most cases, pneumonia is the most chronic flu complication. It tends to be fatal for the elderly and individuals with other serious conditions. 



      Influenza has a high morbidity rate. Many people have been forced to miss work and school. Furthermore, in youngsters and the elderly, the infection can be fatal. People with pre-existing lung illness and diabetes had a greater mortality rate. Overall, the illness can significantly reduce one's quality of life for 1-2 weeks each season.


      When to consult a Physician?

      The majority of people who develop the flu can handle it at home and do not always have to see a doctor. However, if you experience flu symptoms and are concerned about complications, make an appointment with your doctor right away. Antiviral medications can help shorten the duration of the illness and avoid more severe complications.

      In case you are experiencing flu-like symptoms, seek medical attention right away. Adults should be aware of various emergency signs and symptoms such as; 

      • Chest pain 
      • Shortness of breath or breathing difficulties 
      • Constant dizziness 
      • Aggravation of the existing health conditions 
      • Seizures 
      • Muscle pain or extreme body weakness 

      The emergency signs and symptoms of flu in kids can include the following; 

      • Chest pain 
      • Breathing difficulties 
      • Blue lips 
      • Dehydration 
      • Seizures 
      • Chronic muscle pain 
      • Worsening of the already existing health problems


      Bottom Line

      The flu, or influenza, is a viral respiratory illness. Millions of people across the world get ill with the flu every year. It may sometimes result in mild disease. However, it can be more dangerous or even fatal for people above 65 years, newborn babies, and individuals with some chronic diseases. 

      It is caused by a wide variety of influenza viruses. Some of these viruses can infect humans, while others are species-specific. These viruses are spread by respiratory droplets released from the mouth and respiratory system during coughing, talking, or sneezing.

      Touching inanimate things polluted with the virus and touching the nose or eye might spread the influenza virus. Influenza can be transferred before a patient develops symptoms and up to 5 to 7 days after infection.

      More dangerous variants of the influenza virus have emerged during the last several decades. These viruses not only affect people but also animals. Clinicians should be aware that all fast tests for detecting influenza have low sensitivity and frequently provide false-negative findings.

      The PCR test or viral culture of throat secretions is the gold standard for diagnosis, although results take a few days. Vaccination is a critical technique for lowering infection morbidity.

      Luckily, flu is a preventable condition. The best way to ensure that you are free from the virus is by getting a vaccination annually. It’s also essential to practice first-rate health habits such as washing hands regularly and covering the mouth when coughing or sneezing. This can help prevent the transmission of germs and avoid flu. 

      The best way to prevent and treat influenza is with an interprofessional team that comprises a nurse, nurse practitioner, primary care provider, internist, pharmacist, emergency department physician, and infectious disease expert.

      Every year, millions of individuals are affected by the flu, causing them to miss work and school. The symptoms have a negative impact on one's quality of life, and the illness has been known to cause death at extreme ages. The key is to educate patients about immunization. All patients should be urged to acquire the yearly flu vaccination, which is available each November.

      Almost every school has a visiting nurse team that provides pupils with vaccinations. Furthermore, pharmacists are now authorized to provide immunizations to customers who come into a drugstore. The aim is to lower healthcare expenses as a result of individuals flocking to emergency rooms throughout the winter. At the same time, participants have been instructed on the need for hand cleaning, avoiding close contact until symptoms diminish, and drinking enough water.