Swine Flu Symptoms: Signs, Causes, Warning Signs & More

Quick Glance: Common Swine Flu Symptoms

Symptoms can appear suddenly and affect both the respiratory system and the rest of the body when affected with swine flu. Common swine flu symptoms include:

Fever
Tiredness or weakness
Cough
Sore throat
Muscle or body aches
Headache
Reduced appetite
Runny or blocked nose

Swine Flu Symptoms That Should Not Be Ignored

Most swine flu infections reported in people have been mild. However, persistent or worsening symptoms can indicate dehydration, lung involvement or another complication.

The table below highlights swine flu symptoms that should be medically assessed:

Symptom	What It May Indicate
Shortness of breath during normal activity	The infection may be affecting the lungs
Fever or cough that improves and then returns or worsens again	A secondary infection or complication may have developed
Chest discomfort that does not settle	The lungs or airways may need assessment
Repeated vomiting	Ongoing fluid loss can lead to dehydration
Weakness that keeps getting worse	This can happen with a more serious infection or fluid loss
Passing very little urine	Significant dehydration
Worsening asthma or another chronic condition	Influenza aggravating an existing medical condition

Why Do Swine Flu Symptoms Occur?

Swine flu symptoms begin when an influenza A virus infects cells lining the nose, throat and sometimes the lungs. The immune system responds by releasing substances that fight the infection but also contribute to fever, chills, headache, muscle aches and tiredness.

Inflammation in the nose and throat causes congestion and soreness, while airway irritation triggers coughing. If this spreads deeper into the lungs, breathing becomes difficult and pneumonia can develop. Vomiting or diarrhoea may also occur, particularly in children with influenza.

Swine Flu Symptoms That Require Immediate Medical Attention

Serious swine flu complications can affect breathing, hydration, brain function and other vital body processes. Get medical help quickly when the following symptoms appear:

Difficulty breathing or severe shortness of breath
Persistent chest or abdominal pain or pressure
Persistent dizziness, confusion or difficulty waking
Seizures
Little or no urination
Severe weakness or unsteadiness
Fever or cough that improves but then returns or worsens
Worsening of an existing serious medical condition

Symptoms of Swine Flu Based on Type

Human infections can occur from several swine-origin influenza A strains. Because their symptoms are virtually identical, specialised laboratory testing is required to identify the exact virus subtype.

The table below summarises the clinically recognised swine flu subtypes:

Type	Typical Symptoms
Influenza A(H1N1)v	Fever, cough, runny nose, sore throat, body aches, headache and tiredness
Influenza A(H1N2)v	Similar flu-like symptoms, including fever, cough, sore throat and body aches
Influenza A(H3N2)v	Similar influenza-like illness; vomiting or diarrhoea may also occur, particularly in children

Swine Flu Symptoms in Children

Children can develop the same fever, cough, sore throat and body aches seen in adults, but digestive symptoms and changes in behaviour can be more noticeable.

Swine flu symptoms in children that may be noticed by parents include:

Fever
Cough or sore throat
Runny or blocked nose
Tiredness or reduced activity
Poor appetite
Nausea or vomiting
Diarrhoea
Irritability

Fast or difficult breathing, bluish lips or face, ribs pulling in during breathing, seizures, reduced alertness or signs of dehydration require urgent medical attention.

Can You Have Swine Flu Without Symptoms?

Swine flu can sometimes occur without noticeable symptoms. In most people, the infection remains mild and may not even cause a fever.

A person may therefore have only a mild cough, tiredness or throat irritation. Symptoms alone cannot distinguish swine flu from seasonal flu or other respiratory infections. Since it spreads easily from person to person in the community, appropriate laboratory testing (like RT-PCR) and a doctor's clinical evaluation are important when a confirmed diagnosis is needed.

When Can Swine Flu Symptoms Become Life-Threatening?

Swine-origin influenza can become serious when complications interfere with breathing, oxygen delivery, hydration or normal brain and organ function. Severe and fatal cases of swine flu have been reported, although most infections are mild.

The following symptoms may indicate a medical emergency:

Symptom	Why It Is Serious
Severe difficulty breathing or shortness of breath	May indicate pneumonia, reduced oxygen levels or respiratory failure
Persistent chest pain or pressure	May indicate severe lung involvement or another serious complication
Confusion or difficulty waking	May occur with severe infection, reduced oxygen levels or neurological complications
Seizures	May indicate a serious neurological or metabolic complication
Little or no urination	May indicate severe dehydration affecting circulation and kidney function
Severe weakness or unsteadiness	May occur when influenza causes significant systemic illness
Fever or cough that improves and then worsens	May indicate pneumonia or another secondary complication

How are Swine Flu Symptoms Diagnosed?

Swine flu symptoms often overlap with seasonal flu, so doctors consider the pattern of illness, possible exposure and test results before confirming the infection.

The following assessments may help identify the cause:

Test or Assessment	Purpose
Symptom and exposure history	Checks the pattern of symptoms, how quickly they started, and recent contact with other individuals showing flu-like symptoms.
Physical examination	Assesses breathing, temperature, hydration and signs of complications
Influenza molecular test	Detects influenza virus, including influenza A, in a respiratory sample
Specialised variant influenza testing	Helps distinguish swine-origin variant influenza from seasonal influenza A
RT-PCR subtyping or genetic testing	Can confirm and characterise a suspected variant influenza virus

FAQs

Q1. What are the first symptoms of swine flu?

Ans: Swine flu often begins suddenly with fever, cough, sore throat, headache, body aches and tiredness. Some people may also develop chills, a blocked or runny nose, or digestive symptoms such as vomiting or diarrhoea.
Q2. Does swine flu always cause fever?

Ans: No. Fever is a common symptom of swine flu, but it does not occur in every case. A person can still have an influenza infection even if their temperature remains normal.
Q3. Are swine flu symptoms different from seasonal flu?

Ans: No, swine flu (H1N1) and other seasonal flu strains cause almost identical symptoms, including fever, cough, sore throat, and body aches. Because the symptoms overlap completely, laboratory testing (like a nasal swab) is the only definitive way to identify the specific strain of the influenza virus.
Q4. Can swine flu cause vomiting and diarrhoea?

Ans: Yes. Vomiting and diarrhoea can occur with swine flu, although they are reported more often in children. These symptoms can also increase the risk of dehydration, especially when combined with fever.
Q5. What are swine flu symptoms in children?

Ans: Swine flu in children may cause fever, cough, sore throat, tiredness, vomiting and diarrhoea. Poor appetite and irritability may also occur.
Q6. Can swine flu occur without obvious symptoms?

Ans: Yes. Swine flu may cause only mild symptoms, and fever may be absent. Influenza infections can also occasionally occur without noticeable symptoms.
Q7. Which swine flu symptoms need urgent medical care?

Ans: Swine flu symptoms such as difficulty breathing, persistent chest pain, confusion, seizures or severe dehydration need urgent medical attention.
Q8. How do doctors confirm swine flu?

Ans: Doctors evaluate your clinical symptoms and confirm the diagnosis using a molecular laboratory test, such as an RT-PCR swab of your nose or throat. This test detects the genetic material of the virus and can specifically identify if the infection is caused by the H1N1 (swine flu) strain.