Which statements give the correct reasons why smallpox has been eradicated, whereas malaria and cholera have not? 1 Cholera vaccines give immunity for only a short time. 2 Plasmodium antigens alter during the life cycle. 3 Smallpox antigens stay unchanged. 4 Vaccines are effective only against viruses.
- A1, 2 and 3
- B1, 2 and 4
- C1, 3 and 4
- D2, 3 and 4