Science

How do the coronavirus vaccines work?

Since the global outbreak of COVID-19 there has been an urgent search for a potential vaccine. Many classic, well-understood vaccines work by injecting a dead or weakened form of the target virus into the body. This helps the patient build immunity by triggering the immune system response, aiding the body for future recognition and response to the pathogen. The virus introduces the pathogen’s antigens to the immune system, allowing the correct antibodies to be produced, without causing the disease symptoms in the patient. The body retains these antibodies in preparation for further exposures to these diseases. 

The virus responsible for the 2020 global pandemic is termed SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) or more commonly as the coronavirus. It was named corona (Latin for crown) after the club-shaped spike proteins covering the viral surface. The spike antigens are the target of current vaccines being studied by the Oxford Vaccine group, Moderna and Pfizer/BioNTech. These vaccines differ to the classic method previously discussed and employ different platform technologies, with the Oxford vaccine using adenoviral vector technology, while Moderna and Pfizer use mRNA (messenger RNA) technology.

The Oxford adenovirus vaccine works in a partially similar way to the classic vaccine method, as a weakened virus is injected into the bloodstream. However, instead of injecting a weakened form of the coronavirus, Oxford’s vaccine uses the weakened form of a chimpanzee common cold virus (adenovirus) to act as the viral vector called ChAdOx1. The chimpanzee virus is modified to hold the genetic information which codes for the coronavirus spike proteins. So, when a patient is injected, the viral vector ChAdOx1 will produce the spike antigens on its surface triggering the immune system response as previously discussed. 

Two separate mRNA vaccines have been developed by two different groups. Pfizer has collaborated with German biotech company BioNTech to create an mRNA vaccine called BNT162b2. US biotech company Moderna also employed the same technology to find their candidate vaccine mRNA-1273. Taking a step away from the classical vaccination method, patients are injected directly with an mRNA molecule that signals to our cells to present the coronavirus antigens on the cell surface, still triggering the immune response but to our own cells as opposed to viral particles.

Both technologies have been previously studied, in fact the adenovirus vector method is how the seasonal flu vaccine functions. Both types of vaccine require two doses, Pfizer’s three weeks apart while Moderna and Oxford are spread four weeks apart. Storage of the vaccine varies greatly between the three individual vaccines. The Oxford vaccine is easy to store as it can be kept at temperatures between 2°C and 8°C. However, due to the unstable nature of mRNA, the Pfizer and Moderna vaccines are more complicated to store. The single-stranded mRNA genetic information is more likely to break apart above freezing temperatures, creating challenges storing the vaccine. Moderna has an edge over Pfizer here, with the vaccine’s ability to tolerate temperatures of -20°C compared to Pfizer at an astonishing -70°C.

The Pfizer/BioNTech vaccine has been approved for use in the UK and the government secured around 40 million doses of the vaccine. Due to the need of two doses, this is enough for 20 million people to be vaccinated. The NHS began giving the 95% effective Pfizer vaccine on Tuesday 8th December, with top priority given to those most at risk from coronavirus. This includes people who live in care homes as well as care home workers, the over-80s, and health and social care workers. The UK has ordered 5 million doses and reserved 100 million doses of the Moderna and Oxford vaccines respectively, ready for their awaited approval.

15/12/2020

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Sarah Duffy


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