Flu A - Symptoms | Causes | Diagnosis | Treatment | Prevention
Infectious Diseases Data Verified

Flu A - Symptoms, Causes, Diagnosis, Treatment and Prevention

Published on Jun 20, 2022 and last reviewed on Dec 09, 2022   -  4 min read


The flu, or influenza, is a contagious viral infection that attacks the respiratory system. Flu A and B viruses are responsible for seasonal flu epidemics.

What Is Flu A?

The influenza viruses that infect humans are divided into three groups: A, B, and C. Type-A influenza can be deadly, resulting in widespread outbreaks and disease. Common symptoms of type A infection can be mistaken for those of other conditions. While milder cases of influenza can resolve on their own without causing significant symptoms, severe cases of type-A influenza can be fatal.

Influenza viruses are classified into four types: A, B, C, and D. Human influenza A and B viruses cause seasonal epidemics of disease (known as flu season) in the United States almost every winter. The only influenza viruses known to cause pandemics, or global outbreaks of flu disease, are influenza A viruses. A pandemic can arise when a new and distinct influenza A virus appears that can both infect people and spread rapidly among them. Infections with the influenza C virus usually result in mild illness and are unlikely to cause human epidemics. The influenza D viruses primarily affect cattle and have not been found to infect or afflict humans.

The surface proteins of influenza A viruses are used to classify them into subtypes: hemagglutinin (H) and neuraminidase (N). There are 18 different subtypes of hemagglutinin and 11 different subtypes of neuraminidase. The process by which influenza viruses swap gene segments is known as reassortment. When two influenza viruses infect the same host simultaneously, they can swap genetic information. Influenza subtypes A(H1N1) and A(H3N2) are two viruses that commonly circulate in humans (H3N2).

Who Is at a Higher Risk of Developing Flu A?

Most people recover from the flu on their own. However, influenza and its complications can be fatal at times. The following people are at a higher risk of developing flu complications:

What Are the Symptoms of Flu A?

Unlike a common cold, the flu usually has a sudden onset of symptoms. The following are common symptoms of influenza infection:

Symptoms of influenza A may resolve on their own. However, consult the doctor if the symptoms persist for more than a week without improvement. People who are at high risk of flu complications, such as those over the age of 65 or those with weakened immune systems, should seek immediate medical attention. The flu can be fatal in rare cases.

What Are the Causes of Flu A?

When an infected person coughs, sneezes, or speaks, the virus spreads through the air in droplets. A person can either directly inhale the droplets or pick up the germs from an object, such as a phone or computer keyboard, and then transfer them to the eyes, nose, or mouth.

People infected with the virus are likely contagious from the day before symptoms appear until five days after they appear. Children and those with compromised immune systems may be contagious for a slightly extended period.

Influenza viruses are constantly evolving, with new strains appearing on a regular basis. If a person has had influenza in the past, their body has already produced antibodies to combat that particular strain of the virus. Suppose future influenza viruses are similar to those they have encountered previously, either by having the disease or by being vaccinated. In that case, those antibodies may prevent or lessen the severity of infection. However, antibody levels may reduce with time. Furthermore, antibodies against previously encountered influenza viruses may not protect them from new influenza strains, which can be very different viruses from what they had once.

How Is Flu Diagnosed?

The doctor will need to test for the influenza virus before treating the condition. The rapid molecular assay is the preferred test. The physician will swab the nose or throat during this procedure. Within 30 minutes or less, the test will detect influenza viral RNA (ribonucleic acid). However, because the results are not reliable, the doctor may have to make a diagnosis based on the symptoms or other flu tests.

What Are the Treatment Options for Flu A?

With adequate rest and fluid intake, influenza A symptoms may resolve on their own in some cases. In other cases, the doctor may advise taking antiviral medication to combat the infection. Typical antiviral prescriptions include Peramivir, Zanamivir, and Oseltamivir. These medications, known as neuraminidase inhibitors, slow the spread of the influenza virus from cell to cell, thus slowing the infection process. Although these medications are effective, they can cause side effects such as nausea and vomiting. If a person starts experiencing any of these symptoms or if the condition worsens, they must stop taking the medication and see the doctor right away. A new medication called Baloxavir marboxil, developed by a Japanese pharmaceutical company was approved by the United States food and drug administration (FDA). This antiviral medication works to prevent the influenza virus from replicating. Over-the-counter medication can also help with flu symptoms. One must stay hydrated to help loosen mucus in the lungs and strengthen the immune system.

How Can Flu A Be Prevented?

The methods of preventing the spread of this disease include:

  • The best way to avoid the flu is to get vaccinated every year. Each flu shot protects against three to four different influenza viruses during the flu season that year.

  • Handwashing on a regular basis.

  • Avoidance of large crowds, particularly during a flu outbreak.

  • When a person coughs or sneezes, they must cover their mouth and nose.

  • If a person gets a fever, they must stay at home for at least 24 hours after it goes away.


Type A influenza is a contagious viral infection that, if left untreated, can lead to life-threatening complications. While some cases of this infection may improve without the prescribed medication, a trip to the doctor is advised. Patients must not attempt to self-diagnose the condition. The flu can look like a common cold, but it can cause symptoms to worsen. If a person has caught the flu, they must consult their doctor to discuss treatment options.

Frequently Asked Questions


Which Is Worse, Flu Type A or B?

Type A flu is worse than type B flu as it has more severe symptoms than Type B and it is more common. Generally, adults have sufficient immunity against type B flu.


For How Long Does a Person Suffer From Flu Type A?

As per the Centers for Disease Control and Prevention (CDC), type A flu lasts for three to seven days. However, critical complications like pneumonia can be present for a longer time, and a cough may take up to two weeks to go away.


How Fast Does Flu Type A Spread?

Both, type A and type B flu are highly contagious and spread through respiratory droplets. The Centers for Disease Control and Prevention (CDC) claimed that flu viruses can spread to a person from up to six feet away.


How Do You Get Infected By Flu A?

Influenza viruses can travel in the air as droplets and can infect a healthy person when an infected person coughs, sneezes or talks. The droplets can be inhaled by a healthy person or can get transferred from other objects.


What Are the Signs and Symptoms of Influenza A?

Influenza presents with symptoms like runny nose, fever, chills, body aches, sore throat, cough, headaches, fatigue, and chest discomfort.


What Are the Differences Between Flu A and B?

Influenza A and B show similar symptoms but type A flu causes more severe symptoms and is more common than influenza B.


When Is the Condition Alarming for a Child Having Flu?

The condition of a child having flu is alarming when the fever does not respond to medications, rest, and fluids; when the patient feels extreme fatigue, irritability, or has worsening symptoms; and when there is difficulty in breathing or bluish discoloration of the skin (cyanosis).


How Critical Is type A Flu?

Type A flu can be critical and can lead to widespread outbreaks in the community. In mild cases, the disease can go away on its own without showing remarkable symptoms. However, severe cases can turn life-threatening.


Can an Infant Survive the Flu?

Children below 5 years of age are at a higher risk of developing flu complications and those younger than 2 years are at the highest risk. However, the highest hospitalization and mortality rate is noted among infants below 6 months of age.


How Does a Baby With Flu Get Treated?

A baby with the flu will be advised of the following treatment:
- Rest. Help the baby to get a lot of rest by letting him/her sleep as often as possible and promoting lots of quiet activities during the day.
- Increased intake of fluids to prevent dehydration from fever and loss of appetite.
- Painkillers.
- Antiviral medications.


What Is the Incubation Period for the Flu?

The general incubation period for the flu is one to four days. However, the average incubation period is two days.


Can a Person Get Exposed to Flu and Not Catch It?

There are minimal chances of getting exposed to the flu and not catching it. However, taking annual flu shots, practicing good hand hygiene, and avoiding touching of mouth, nose, and eyes can help in preventing it.

Last reviewed at:
09 Dec 2022  -  4 min read




Comprehensive Medical Second Opinion.Submit your Case

Related Questions & Answers

How to avoid cold and flu after winter workout?

Query: Hello doctor, I like to go running. I was a very successful marathon runner when younger. Now I still workout, but my goal, apart from general health is mostly emotional fitness for the job. I work on the phone with customers and I have to be in a strong positive mood to be successful. I am currentl...  Read Full »

Can flu happen anytime or only during a particular season?

Query: Hi doctor, I have had flu ever since I was three. I am now sixteen, but the flu happens all year round. The flu comes early in the morning after waking up and at night before sleep, and also when I wake up abruptly—my nose and eyes itches. My nose is also congested, and I can only breathe thr...  Read Full »

Cold and Flu - Causes, Symptoms, Diagnosis, Treatments

Article Overview: The terms cold and flu are used interchangeably in many contexts. Although both are viral infections, they are caused by different types of virus and symptoms are slightly different in each. It is important to know the difference in order to take measures early and avoid complications. This article gives you an idea on how to effectively deal with cold and flu. Read Article

Velusamy Madathupalayam Palansamy
Velusamy Madathupalayam Palansamy
Dietician, Homeopathy, Surgical Gastroenterology

Introduction While a cold is often wrongly referred to as flu, they are both quite different. Both the infections are caused by different types of virus, and symptoms vary as well. Both the infections are more common during the winters and are contagious, that is, it can spread from one person to an...  Read Article

Popular Articles Most Popular Articles

Do you have a question on Flu A or ?

Ask a Doctor Online

* guaranteed answer within 4 hours.

Disclaimer: No content published on this website is intended to be a substitute for professional medical diagnosis, advice or treatment by a trained physician. Seek advice from your physician or other qualified healthcare providers with questions you may have regarding your symptoms and medical condition for a complete medical diagnosis. Do not delay or disregard seeking professional medical advice because of something you have read on this website. Read our Editorial Process to know how we create content for health articles and queries.