How the AstraZeneca Covid vaccine works? A simple overview

Vaccine against covid19

A vaccine for global affordable distribution

The vaccine that is said to be the first to arrive in South Africa is the so-called ‘Oxford vaccine’. The research for this vaccine was done at Oxford University with the pharmaceutical company AstraZeneca (a well-known company with a good reputation) and with financial backing by both the UK and US governments.  One of the key objectives of Oxford-AstraZeneca is that the vaccine should, in principal, not be for profit, but rather for global, affordable distribution.

AstraZeneca vaccine has been thoroughly tested

AstraZeneca vaccine has been developed by scientists and doctors and has been tested thoroughly in humans. It has passed all the necessary clinical trials and regulatory reviews that are required of human medications. Although this process happened in a shorter time than usual for vaccine development, no shortcuts were taken in the process.  At one point, the trials were halted because some patients seemed to acquire bad side effects. However, each of these cases was thoroughly studied and in every one, the patient’s condition was found not to be linked to the vaccine, and so the trials continued. This vaccine is relatively easy to produce. It is being produced in India, where 60% of the world’s vaccines are already produced and where they already have the special facilities required to safely manufacture this vaccine. It is called Covishield.

How does the AstraZeneca vaccine work?

Viruses are non-living organisms. They cannot multiply on their own. They have to get themselves INSIDE a host cell where they hi-jack the host’s protein-making devices to make more of their components and then assemble new viruses.

A vector vaccine

In this type of vaccine, another virus (one that cannot cause illness in humans), is used as a carrier or “vector”. The vector transports the vaccine component into the cell. Only the gene of the Spike Protein (a part of the COVID virus’s outer coat) of the SARS-CoV2 virus is put inside the carrier virus.  This single gene of the SARS CoV2 virus cannot cause illness in us because it is only one tiny part of the outer shell of the COVID virus. At this point the gene is well hidden inside the carriers. The process is simple:

  • Once injected,  the carrier virus goes into our bodies and attaches to our cells.
  • They then push the Spike Protein gene into our cell.
  • Our cells’ protein-making parts then make hundreds of copies of these Spike Proteins.
  • These hundreds of Spike Proteins are released into our body.
  • They are recognised as foreign or “not self” and are destroyed by our immune system.
  • The immune system remembers this response and keeps the mechanisms at hand in case it sees the protein again.

How the vaccine creates immunity?

Immunity is very complicated but in essence there are 3 steps:1) Recognise the invading “germ” – in this case the SARS CoV-2 virus,2) Make specific antibodies that destroy the invader, and3) Make memory cells so it can recognise the invader quickly if it comes into the body again. If it’s the first time your immune system has ever seen a foreign “germ”, steps 1 and 2 take time and use lots of energy. During this time the germ makes you sick. How sick you get, depends on the type of germ and how strong your immune system is in making new antibodies. Your immune system then goes on to make memory cells as you get better. The point of a vaccine, is to stimulate ALL THREE steps of the immune response WITHOUT the person getting sick. In the case of the Covishield vaccine, by only giving an outer coat Spike Protein of the SARS CoV2 to the patient and not the whole virus, it is impossible to get COVID illness by having a vaccine. However, your immune system learns to recognise the Spike Protein as bad and creates antibodies to kill it. A vaccine should, most importantly, stimulate your immune system to memorise and be able to instantly recognise these specific Spike Proteins if they enter the body in the future. Steps 1 and 2 can then kill the now-known virus, usually before it makes you sick. If you do have symptoms these are likely to be mild.

How effective is the AstraZeneca vaccine?

  • How safe are you once you take the vaccine?
    The medical trials show that the vaccine produces 74 – 90 % immunity against future SARS CoV2 virus invasion in an immunised person.
  • Does Covshield offer immunity for new strains of Covid-19?
    Trials are continuing to establish this vaccine’s effectiveness against the new variants of the virus. At this point it seems there is at least some immunity to variants.
  • Should you take the vaccine if you have had Covid-19 before?
    If you have had COVID illness before, it is still worth having the vaccine because it ensures even better memory in your immune system.
  • How many doses of the Covshield is necessary?
    A person needs 2 doses of the vaccine, 4 to 12 weeks apart to ensure production of memory immunity.
  • How must the vaccine be stored?
    The injection is stored at a normal fridge temperature of 2 – 8degrees Celsius (an advantage over the Pfizer and Moderna vaccines that both require specialized storage facilities).
  • Is the injection painful? Where is it given?
    The injection is given in the upper arm. A patient may experience localized pain & redness and some may get some mild COVID-like symptoms as their immune system works to recognise and kill the invader (this is the same with any vaccine). As is the case with all vaccines, it is possible to have an anaphylactic reaction to the vaccine. This is also very rare and can be easily managed.
  • Is the vaccine safe for everyone? What about breastfeeding or pregnant women, children, or patients with allergies or other underlying issues?The vaccine is approved for adults (people over the age of 18). At this stage, it is not recommended in pregnant or breastfeeding women or in children, as the clinical trials have not yet been done in these groups.If you are allergic to a component of the vaccine, you also cannot have it. Fortunately this is very rare. It is safe to give to immunocompromised and immunosuppressed patients, on advice by their doctor, although they may have a weaker overall immune response.

In conclusion

Ongoing trials are being conducted on this and other vaccines around the world in order to get more detailed information on all aspects of the vaccines. But think about this: Currently, the COVID mortality rate is 2%, (i.e. 2 or 3 people per 100 infected are dying) and many more are being permanently disabled by the COVID infection. On the other hand, of the 11500 people in the Oxford-AstraZeneca vaccine trials, not one person has died and side effects have been minor.

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Dr Lauren Wise

Dr Lauren Wise

Dr Lauren Wise, a general practitioner working in Bedfordview (MBBCh, DCh, DA, Dip Obs). She is a member of GGPC (Gauteng General Practitioners Collaboration) which has created a platform for doctors to share resources during Covid-19. Look for #voicesthatcare on the GGPC Facebook page.

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