Which of the following statements is/are correct about vaccination that provides protection against an infectious disease? 1. It blocks the entry of the infectious agent into body. 2. It produces antibodies against infection. 3. It kills the infectious agent when it enters in the body.

Vaccination works on the principle of immunological memory. When a vaccine (containing weakened, killed pathogens or antigenic parts) is administered, the immune system produces antibodies against it without causing the disease. On subsequent exposure to the actual pathogen, the body can mount a rapid antibody response. Vaccines do NOT physically block entry of pathogens into the body (statement 1 incorrect), nor do they themselves directly kill infectious agents (statement 3 incorrect) — the killing is done by the immune response triggered by the antibodies and memory cells. Hence only statement 2 is correct.