Sindiso Marume holding her brother's health card. Image credit

Sindiso Marume holding her brother’s health card. Image credit

ZIMSEC O Level Combined Science Notes: Disease:Immunity and Immunisation

  • Immunity-is the ability of the body to resist diseases
  • There are various types of immunity:
Type of ImmunityHow it is acquired
Naturally acquired active immunity
  • Antigens enter the body naturally resulting in the body being stimulated to produce antibodies against a specific antigen leading to recovery.

  • That information gets stored in the brain for use if the body is exposed to the same infection in future

  • This has a long term effect
Artificially acquired active Immunity

  • Antigens introduced into the body by means of a vaccine

  • The body, through trial and error, eventually produces the corrent antibodies against the antigen

  • The information is stored for future use by the brain to allow for fast recovery if the body is exposed to a similar infection in the future

Naturally acquired passive immunity

  • Receiving ready-made antibodies as in the case with infants when they receive antibodies from their mothers:

  • Through the placenta before birth

  • Through breastfeeding after birth

Artificially acquired passive immunity

  • Obtained by injecting a serum containing antibodies into the body

  • This is a form of immunity that is given when there is risk of infection and there would be no time for the body to produce its own antibodies before the symptons of the infection are felt/death occurs

  • The serum isprpared from the blood of an animal e.g. a horse/mouse that is activiley immunised

  • The plasma of the animal is collected other elements are removed leaving only the antibodies

  • Antigen-is any substance that causes the body’s immune system to produce antibodies against it
  • It may be a foreign substance from the environment such as bacteria, chemicals, viruses, pollen etc
  • Or it may be formed within the body for example toxins produced by bacteria
  • Antibodies/Immunoglobulin- is a special protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses

Immunisation of infants

  • Is important to prevent them from contracting diseases such as polio, measles etc
  • By Zimbabwean law all infants are required to be artificially immunised against certain diseases as shown below
Primary Courses

  1. Birth

  2. 3 Months

  3. 4 Months

  4. 5 Months

  5. 9 Months

  6. 18 Months

  7. 5 years

  • BCG (Against Tuberculsis/TB)

  • DPT1,Polio 1

  • DPT2,Polio 2

  • DPT3,Polio 3

  • Measles

  • DPT and Polio

  • BCG, DT, Polio


  1. Girls 10-14 years

  2. Girls and boys at 13 years

  3. 15-19 years

  • Rubella(German measles)

  • Tuberclosis

  • Tetanus, Polio

NB In the acronym DPT-

  • D-Diphtheria
  • P-Pertussis/ Whooping Cough
  • T- Tetanus
  • The BCG immunisation will be repeated if there is no scar after 3 months
  • BCG is used against diseases such as meningitis, TB, miliary disease

To access more topics go to the Combined Science Notes page