The COVID-19 vaccine, how are we actually doing?

What is COVID-19?

COVID-19 is the disease caused by a novel strain of coronavirus, believed to have emerged through zoonotic transmission from bats in Wuhan, China. The coronavirus, named SARS-CoV-2 (Severe Acute Respiratory Syndrome-Coronavirus) due to its similarity to the SARS virus which emerged in 2003 in southern China, is responsible for the pandemic currently affecting the global population.

Social distancing, compulsory masks, self-isolation and quarantine are some of the measures in place which aim to prevent the spread of the virus and hence limit the number of deaths. However, it has been suggested several times that in order to return to normal life, a vaccine is necessary – something which we are ever-nearer approaching.

What does the virus look like?

The virus has a positive, single-stranded, RNA genome, enveloped by a membrane with protruding S-proteins (Image 1). The S-protein is made up of two subunits; the first of which binds to cell receptors on the lungs and the second of which allows entry into the cell.

Image 1: SARS-CoV-2 Virus, with the S-protein labelled.

How do COVID-19 vaccines hope to prevent disease?

The aim of the vaccine is to elicit an immune response against the S-protein. In binding to the S-protein, the virus is unable to enter cells and hence an individual cannot become infected. In the event that an individual is exposed to SARS-CoV-2, the immune system can then act rapidly, preventing disease (Image 2).

Image 2: Illustration of how the vaccine prevents diseases, through eliciting the S-protein antibodies which bind upon exposure to the virus preventing disease.

The two main vaccine runners thus far are the Pfizer vaccine and the Oxford vaccine (Image 3):

1. The Pfizer vaccine works by inserting mRNA into the cell, which is then translated to S-protein and presented on the outside of the cell. These proteins are recognised by the immune system as foreign, and antibodies are released to bind to the cell.

2. The Oxford vaccine uses a different approach; injecting a modified version of chimpanzee adenovirus that is unable to cause disease in humans, with SARS-CoV-2 S-protein on its surface. This too elicits an immune response with antibodies against the S-protein.

Image 3: Illustration of the Pfizer vaccine and Oxford vaccine, which prime the body to produce S-protein antibodies through mRNA and viral-vectors, respectively.

Where are we up to?

The Pfizer vaccine is the first vaccine to reach phase III trials and has produced, in the early stages, very promising results. However, it is important to remember that only press releases and no official papers have been released thus far. Despite the hope instilled by this news, we must remember, as Prime Minister Boris Johnson said earlier this week, it is ‘very, very early days […] cannot rely on this as a solution’. The Oxford vaccine is also looking promising with results from its phase III trials to be published soon.

What will happen after a vaccine is approved?

Approval is only the first step; the vaccine then needs to be mass-produced and administered to billions of people on the planet in order to achieve herd immunity. It also needs to be made accessible to everyone, including those in remote areas. In the UK, a list those receiving the vaccine first has been released, starting with the most vulnerable. Additionally, we do not know the degree of immunity that this vaccine provides, including whether it will prevent the disease entirely or reduce disease, nor how long immunity will last. These are questions that only time can answer.

By Sarah Baum

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