| 1. | Immediate elimination of pathogens |
| 2. | Use of physical barriers to prevent infections |
| 3. | The memory of the immune system to produce antibodies on subsequent exposure |
| 4. | Use of cytokines to block viral replication |
| 1. | By using live, attenuated hepatitis B virus |
| 2. | By using recombinant DNA technology to produce antigenic polypeptides of the virus in yeast |
| 3. | By extracting antibodies from infected individuals |
| 4. | By using inactivated viral particles obtained from infected patients |