B2.2 What are vaccines and antibiotics and how do they work?

B2.2 What are vaccines and antibiotics and how do they work?


VACCINATION involves exposing the body’s immune system to a weakened or harmless version of the pathogen in order to stimulate white blood cells to produce antibodies. If the body is re-infected by the same microorganism, memory cells produce antibodies quickly so that the microorganism is destroyed before damage is done. This is how vaccination works:

Injection of vaccine


A safe form of the diseases – cause microorganism is injected into the body


Immune response triggered

Although the microorganism is safe, the antigens on its surface still cause the white blood cells to produce specific antibodies


Memory cells remain in body

Long after the vaccination, memory cells patrol the body. If the disease-causing microorganism infects the body again, the white blood cells can attack it very quickly.


In order to prevent an EPIDEMIC of a disease in a population it is important that as many as individuals as possible are vaccinated. If more than 95% of the population is vaccinated then the unvaccinated will be protected too because the risk of coming in contact with an infected person will be very small.


There is no guarantee that all vaccines and drugs (medicines) are risk free. People have GENETIC DIFFERENCES, so they may react to a vaccine or a drug in different ways – these are called SIDE EFFECTS.

ANTIMICROBIALS are chemicals that kill, or inhibit bacteria, fungi and viruses. ANTIBIOTICS are a type of antimicrobial that are only effective against bacteria but NOT viruses


Over a period of time, bacteria can become RESISTANT to antimicrobials.

MUTATIONS (random changes) can take place in the genes of microorganisms. This leads to new strains of bacteria and fungi that are no longer affected by the antimicrobial. These reproduce and pass on the resistance – as a result, the antimicrobial is no longer effective.


To prevent resistance to antimicrobials increase:


  • Doctors should only prescribe them when completely necessary
  • Patients should always complete a course of antibiotics, even if they are feeling better.