Edexcel IGCSE Biology 复习笔记 2.8.9 Vaccinations

Edexcel IGCSE Biology 复习笔记 2.8.9 Vaccinations

Vaccinations

 

  • Vaccines are used to induce immunity to infectious diseases
  • A vaccine contains harmless versions of a pathogen
  • There are several different methods by which scientists ensure that vaccines contain harmless pathogens such as:
    • Killing the pathogen
    • Making the pathogen unable to grow or divide (attenuated vaccine)
    • Using fragments of pathogens, rather than whole cells

     

  • A vaccine may be administered orally, nasally or via an injection

 

 

 

How vaccines work

  • Once in the bloodstream, the antigens contained within the vaccine can trigger an immune response in the following way:
    • Lymphocytes recognise the antigens in the bloodstream
    • The activated lymphocytes produce antibodies specific to the antigen encountered
    • Memory cells and antibodies subsequently remain circulating in the blood stream

     

 

 

 

Vaccination

 

The process of long-term immunity by vaccination

 

 

 

  • Future infection by the same pathogen will trigger a response that is much faster and much larger compared to the initial response
  • Due to the rapid nature of the response, the pathogen is unable to cause disease and the individual is said to be immune

 

 

 

Vaccination-graph

 

Graph showing the number of measles antibodies in the blood following vaccination. The secondary response is much faster and a greater number of antibodies are produced.

 

 

 

The importance of vaccination

  • Vaccines not only protect the vaccinated individuals, they also reduce the likelihood that an infected individual will spread the pathogen to others
    • If a large proportion of the population is vaccinated, it is unlikely that an unvaccinated individual will become infected with the pathogen (this concept is referred to as herd immunity)
    • This can prevent the spread of the disease

     

  • Vaccines have reduced the cases of certain diseases drastically or even eradicated many diseases worldwide
    • This includes smallpox, measles, mumps and tetanus amongst many others

     

  • There are hopes for the future eradication of several other diseases through vaccination programs
    • This includes polio, HIV, malaria and of course COVID-19

     

 

 

Disadvantages of vaccinations

  • There are some disadvantages to vaccinations that reduce how effective vaccination programs can be
    • Mutations in the pathogen's DNA/RNA can result in significant changes to the antigen of the pathogen meaning that lymphocytes no longer recognise the pathogen
    • Side-effects of vaccinations can reduce the uptake in the population

     

 

 

Advantages & Disadvantages of Vaccination TableAdvantages-and-disadvantages-of-vaccination-table

转载自savemyexam

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