Developing a vaccine for Covid-19

Case study four: COVID-19

The coronavirus pandemic that started in the Wuhan province of China at the end of 2019 continues to spread rapidly across the globe through 2020, causing a high number of deaths and societal disruption.

At the time the pandemic was declared no effective vaccine existed, but within months several groups around the world were working on potential vaccines and at the time of writing there are several vaccines that are ready to go in early trials in humans. To make a vaccine for a new virus it is not as simple as taking a vaccine that is already in use and adapting them. New vaccine types are needed. Examples of the types of vaccine being developed are listed below, but these vaccines are all yet to be shown to be effective.

RNA Vaccines

RNA is genetic material found in human cells that is coded to tell cells what to build. RNA vaccines contain a code that will enable cells to build antigens from the target pathogen which the body then mounts an immune response to. This immune response is the basis of the immunity provided by this vaccine type.

Recombinant Protein Vaccines

Many of the existing vaccines that protect against viral infections contain weakened versions of the live virus such as MMR. This is not possible for all infections as in some cases weakening the viruses means that they do not produce a good enough immune response in the body. Synthetic production of the key antigens from the pathogen of interest are used in recombinant vaccines. The advantages of this vaccine type are that the synthetic products are not infectious and the key parts that stimulate the immune system are better preserved compared to the weakened viruses.

Vector Vaccines

Genetic material from the infectious agent for which a vaccine is required is incorporated into an unrelated virus which then acts as carrier or vector of the genetic material. Once in the body some viral vectors can be modified to multiply in a harmless way increasing the amount of ‘vaccine’ available and also stimulate the immune system in their own right improving the overall response to the vaccine. Non-replicating viral vectors are also used. This helps make them safe for people at the extremes of age or with underlying medical problems.

Monoclonal Antibodies

Antibodies that are directed against a particular infectious disease can be used to prevent or treat infection. This is called passive immunisation as the body does not produce the antibodies or an immune response like other types of immunisation. The antibody is made synthetically based on the pathogen structure. The main limitation of passive immunisation is that it only lasts for a few weeks.

Next we will look at antimicrobial resistance and what role vaccines can play in reducing the inappropriate use of antimicrobials.