A vaccination programme against a childhood disease began in year 5. The graph shows the number of reported cases of the disease.
Using the graph, describe how the number of cases changed between year 5 and year 15.
[2]
The disease almost disappeared even though not everyone was vaccinated. Explain how the vaccination programme protected people who were not vaccinated.
[3]
After year 15 the number of cases rose again. Suggest an explanation for this rise.
[2]