A vaccine against a bacterial disease is being tested in sheep.
An antibody concentration of at least 20 µg per cm³ is needed to prevent symptoms when a sheep is exposed to the bacterium.
The sheep were put into two groups at random. Programme A involved one injection on day 0. Programme B involved injections on day 0 and day 28.
| Day | Mean antibody concentration with programme A in µg per cm³ | Mean antibody concentration with programme B in µg per cm³ |
|---|---|---|
| 28, before the second injection | 12 | 12 |
| 35 | 9 | 56 |
| 84 | 2 | 27 |
Using the data and your knowledge of vaccination, explain why programme B is expected to prevent symptoms more effectively if the sheep are exposed to the bacterium on day 84.
252 exam-style questions on AQA GCSE Biology 3.1 Communicable diseases, covering 3.1.1 Communicable (infectious) diseases, 3.1.2 Viral diseases, 3.1.3 Bacterial diseases, 3.1.4 Fungal diseases, 3.1.5 Protist diseases, 3.1.6 Human defence systems, 3.1.7 Vaccination, 3.1.8 Antibiotics and painkillers, and 3.1.9 Discovery and development of drugs. Each one has a worked solution and a mark scheme showing where the marks go.