The smallpox vaccination programme was a major achievement in medicine, and it led the World Health Organisation to declare in 1980 that the world was free of smallpox. Which statement most accurately shows why the smallpox vaccination programme was successful?
- AThe virus also infected animals making it easy to stop the transmission cycle.
- BThe virus remained in the body following infection and could become active later.
- CThe virus was stable and not prone to mutations.
- DThe virus was unstable and prone to mutations.