How Vaccines Work (Cambridge International AS Biology)

Spec point — 11.2.5 · explain that vaccines contain antigens that stimulate immune responses to provide long-term immunity

How vaccines work

• A vaccine is a suspension of antigens that are intentionally put into the body to induce artificial active immunity

  • A specific immune response where antibodies are released by plasma cells

• There are two main types of vaccines:

  • Live attenuated*
  • Inactivated

• Vaccines are administered either by injection or orally (by mouth)

  • When a person is given a vaccine they have been given a vaccination(they are said to have been vaccinated)

• Vaccinations given by injection are usually into a muscle or under the skin

• Vaccinations produce long-term immunity as they cause memory cells to be created

  • The immune system remembers the antigen when reencountered and produces antibodies to it, in what is a faster, stronger secondary response

The process of vaccination and development of long term immunity

Live attenuated vaccines

• Live attenuated vaccines contain whole pathogens(e.g. bacteria and viruses) that have been ‘weakened’

  • These weakened pathogens multiply slowly allowing for the body to recognise the antigens
  • They trigger the primary immune response (plasma cells to produce antibodies)
  • These vaccines tend to produce a stronger and longer-lasting immune response

Inactivated vaccines

• Inactivated vaccines contain whole pathogens that have been killed (‘whole killed’) or small parts (‘subunit’) of the pathogens (e.g. proteins or sugars or harmless forms of the toxins – toxoids)

  • As inactivated vaccines do not contain living pathogens they cannot cause disease, even for those with weak immune systems

  • However these vaccines do not trigger a strong or long-lasting immune response like the live attenuated vaccines

    • Repeated doses and / or booster doses are often required

Exam Hint Remember vaccines trigger the primary immune response (T-helper cells trigger plasma cells to secrete specific antibodies), which leads to the production of memory cells. This will give a faster and greater response (a higher concentration of antibodies in a shorter period of time) during the secondary response.