What is vaccine and how are they developed?

•scientists, industry and other organisations have worked collaboratively across the globe to complete the different phases of vaccine development in parallel, rather than sequentially to make a safe and effective vaccine available as soon as possible•

•by knowing the genetic code for the SARS-CoV-2 virus, various methods to create vaccines can be used such as using the code itself (mRNA vaccines) or inserting part of this code into existing viruses (viral vector vaccines)

•by December 2020, over 270 different COVID-19 vaccines were in early development, over 50 of these were being given to people in clinical trials and 11 were being trialled in large phase 3 trials

•some vaccines have been made using currently used vaccine technology, others have been made using new approaches or methods used during previous emergencies such as the SARS pandemic and west African Ebola

What are the properties that are looked for when deloping a vaccine?

Ideally, a vaccine will:

•produce the same immune protection which usually follows natural infection but without causing disease.

•generate long lasting immunity so that the person is protected if they are exposed to the antigen several years after vaccination.

•interrupt the spread of infection by preventing carriage of the organism in the vaccinated person

Vaccines need to be safe and the risk from any side effects should be much lower than the benefit of preventing deaths and serious complications of the disease.

For the COVID-19 vaccines, many of these properties can be confirmed from the clinical vaccine trials.

Longer term ongoing surveillance of the disease and of those vaccinated will show whether:

•vaccine protection is long lasting or booster or annual doses are needed

•the vaccine prevents a vaccinated person from carrying and spreading the virus

Which vaccines are being used?

On 2 December 2020, the following vaccine was given authorisation for temporary supply by the UK DHSC and the MHRA:

COVID-19 mRNA Vaccine BNT162b2 (Pfizer-BioNTech) is a messenger ribonucleic acid (mRNA) that contains the genetic sequence of the antigens found on the surface of the SARS-CoV-2 virus. This is the first vaccine to be rolled out, and the one that will be used in the first waves of the immunisation program.

The COVID-19 mRNA Vaccine BNT162b2 vaccine is a messenger ribonucleic acid (mRNA ) vaccine. It contains the genetic sequence (mRNA) for the spike protein which is found on the surface of the SARS-CoV-2 virus, wrapped in a lipid envelope (referred to as a nanoparticle) to enable it to be transported into the cells in the body. When injected, the mRNA is taken up by the host’s cells which translate the genetic information and produce the spike proteins. These are then displayed on the surface of the cell. This stimulates the immune system to produce antibodies and activate T-cells which prepare the immune system to respond to any future exposure to the SARS-CoV-2 virus by binding to and disabling any virus encountered. As there is no whole or live virus involved, the vaccine cannot cause disease. The mRNA naturally degrades after a few days.

Another COVID-19 vaccine which may shortly be authorised for supply in the UK, subject to regulatory approval, is:

AstraZeneca COVID-19 vaccine which is a non-replicating viral vector vaccine. It uses a weakened adenovirus as a carrier to deliver the genetic sequence for part of the SARS-CoV-2 virus into the body. This is not yet available, and as such will not be used in the first waves of the program.

AstraZeneca COVID-19 vaccine is a viral vector vaccine which uses a weakened adenovirus as a carrier to deliver the SARS-CoV-2 antigen. The adenovirus has been modified so that it cannot replicate (grow and multiply by making copies of itself) in human cells and therefore cause any disease. The genes that encode for the spike protein on the SARS-CoV-2 virus have been inserted into the adenovirus's genetic code to make the vaccine. When the vaccine is injected, it enters the host's cells which then manufacture the spike protein. This then stimulates the immune system which reacts by producing antibodies and memory cells to the SARS-CoV-2 virus without causing disease.

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