Interpandemic period |
1 | No new influenza virus subtypes detected in humans | |
2 | Animal influenza virus subtype poses substantial risk | UK not affected |
| | UK has strong travel/trade connections with affected country |
| | UK affected |
Pandemic alert period |
3 | Human infection(s) with a new subtype, but no new human to human spread to a close contact | UK not affected |
4 | Small cluster(s) with limited human-to-human transmission but spread is highly localised, suggesting that the virus is not well adapted to humans | UK has strong travel/trade connections with affected country |
5 | Large cluster(s) but human-to-human spread still localised, suggesting that the virus is becoming increasingly better adapted to humans | UK affected |
Pandemic period |
6 | Increased and sustained transmission in general population | Alert level | |
| | 1 | Virus/cases only outside the UK |
| | 2 | Virus isolated in the UK |
| | 3 | Outbreak(s) in the UK |
| | 4 | Widespread activity across the UK |
Post pandemic period |
| Return to interpandemic period |