Influenza
Also known as Flu, Seasonal influenza
This article is general health information for the selected condition. It is not a diagnosis and does not replace clinical judgement. If you have questions or need treatment advice, please consult a qualified healthcare professional.
What is influenza?
Influenza is a contagious respiratory infection caused by influenza viruses. It differs from a common cold by its abrupt onset, prominent fever and severe muscle aches, and it can be dangerous for older adults, pregnant people and those with chronic disease. Annual vaccination is the most effective preventive measure because the virus changes each season.
Causes
- Influenza A and B viruses
- Spread by respiratory droplets and aerosols
- Contact with contaminated surfaces
- Antigenic drift causing seasonal change in circulating strains
Symptoms
- Sudden onset fever and chills
- Prominent muscle and joint aches
- Headache
- Dry cough and sore throat
- Marked fatigue that can persist for weeks
- Nasal congestion
- Vomiting and diarrhoea, more often in children
Risk factors
- Age over 65 or under 5
- Pregnancy
- Chronic heart, lung, kidney or liver disease
- Diabetes
- Weakened immune system
- Obesity
- Residential care settings
Diagnosis
- Clinical diagnosis during known influenza season
- Rapid antigen or PCR testing of a nasal or throat swab
- Chest X-ray if pneumonia is suspected
- Pulse oximetry in those who are unwell
Treatment
- Annual vaccination for prevention
- Rest, fluids and antipyretics for most people
- Antiviral medicines such as oseltamivir for high risk groups, ideally within 48 hours
- Hospital care for severe illness or complications
- Antibiotics only if secondary bacterial infection develops
- Staying home to reduce transmission
Self care
- Rest and drink fluids regularly
- Use paracetamol or ibuprofen for fever and aches
- Stay home to avoid infecting others
- Cover coughs and wash hands frequently
- Expect fatigue to persist for one to two weeks
- Seek antiviral treatment early if you are in a high risk group
When to see a doctor
Book an appointment if:
- Symptoms worsening after initial improvement
- Fever lasting more than five days
- Breathlessness or chest pain
- Being in a high risk group, ideally within 48 hours of onset
- Pregnancy with influenza symptoms
- Existing lung, heart or immune conditions
Some symptoms need emergency care rather than an appointment. See the warning signs listed above.
Prevention
- Annual influenza vaccination, especially for high risk groups
- Good hand hygiene
- Stay home when unwell
- Cover coughs and sneezes
- Vaccination in pregnancy protects both mother and baby
Outlook
Most healthy adults recover fully within one to two weeks, though cough and fatigue can linger longer. Complications such as pneumonia are more likely in older adults, pregnant people, young children and those with chronic disease, and this group benefits most from vaccination and early antiviral treatment.
Common questions
How is flu different from a cold?
Colds start gradually with a runny nose and mild symptoms. Influenza typically begins abruptly with fever, severe aches and exhaustion that puts people to bed, and it carries a real risk of complications.
Why is the vaccine needed every year?
Influenza viruses change continuously, so the vaccine is reformulated each season to match circulating strains. Immunity also wanes over months, making annual vaccination necessary.
Can the flu vaccine give you flu?
No. Injected vaccines contain inactivated virus or a single protein and cannot cause infection. Mild soreness, low grade fever or aches for a day or two reflect the immune response, not influenza.
References
Important: Dard AI is not a medical device and does not diagnose, treat, or replace clinician judgement. This article is general information only. Always consult a qualified healthcare professional about diagnosis and treatment, and seek emergency care for severe or rapidly worsening symptoms.