Flu (influenza) is usually most contagious from about a day before symptoms start through the first few days of illness. Many people remain infectious for around 5–7 days after symptoms begin; children and people with weaker immune systems may shed virus longer. This guide is general UK information — book GP Carely if you need personalised advice or a fit note.
Typical contagious window
Adults often stop being highly contagious around a week after symptoms start, especially once fever has settled for 24 hours without medicine. Exact timing varies. Stay home while feverish or very unwell, cover coughs, and wash hands.
Flu is not the same as a cold or COVID-19. Testing is not always needed for mild illness.
When to seek urgent care
Call 999 for severe breathing difficulty, chest pain, confusion, blue lips, or if you cannot keep fluids down and feel severely unwell. High-risk groups (pregnancy, heart/lung disease, immunosuppression) should seek advice sooner.
Work and fit notes
Many employers accept self-certification for short absences. If you need a GP fit note, book an online consultation after clinical assessment.
Frequently Asked Questions
Can I go to work with flu?
Avoid work or school while feverish and very contagious. Follow your employer’s policy and public health advice.
Do I need antibiotics for flu?
Flu is viral. Antibiotics do not treat viruses. A GP can advise if a secondary bacterial infection is suspected.
Medical notice: online GP care does not replace emergencies — call 999 for life-threatening symptoms. Clinical documents are only issued after a professional consultation. Policies, doctor profiles, privacy and terms are available on this site.
GP Carely — www.gpcarely.com — UK telemedicine platform connecting patients with GMC-registered GPs.