Coronavirus vaccines

COVID-19 has infected over 16million people worldwide and over 4 million in the US at the time of writing with deadly consequences. It is vital therefore to find not only adequate treatments but also preventative methods to prevent the spread of the disease. Vaccines work to prevent diseases by priming our immune systems against invaders. They classically contain viral proteins called antigens or weakened forms of the virus with antigens on the surface. New methods are attempting to use DNA/RNA (genetic material). These will then be made into protein antigens in cells. As a result of this exposure to antigens, we produce proteins called antibodies that can recognize them. When we next encounter the virus, our antibodies attach to these antigens, and the virus is marked out for clearance by the body. Crucially we avoid developing illnesses in the first place. Vaccines are useful in our toolkit alongside treatment methods such as antivirals and post-infection therapies, as we discuss in another article.

COVID-19 vaccine challenges

Developing a vaccine that works and can be delivered timely is a difficult process. Typically new medicines take at least 5 years and more often 10 years to develop. Several phases of testing need to take place, toxicities monitored and optimal doses found. Testing processes have been streamlined and organizations are being encouraged to collaborate such that we can hopefully expect a vaccine by early 2021.

Nevertheless, only around a fifth of medicines in early testing reach the final stages of approval and marketing, for vaccines this even higher at only around 10% in phase III trials. Many fail due to unforeseen side effects and others simply because they have inadequate efficacy. Plus we are still learning about this virus as it is novel. It is hoped that with multiple potential vaccines at least one will be successful. Over 200 are in development, 24 are being tested and of these 2 have reached trial phases II/III.

It is also worth noting that vaccines are not one size fits all. The route of administration, suitability for the young, elderly, and immunocompromised needs to be assessed. Live vaccines, for example, may not be suitable for these groups of people or they may need additional doses to develop immunity if the vaccine is suitable.

Other problems include the time needed to produce and distribute the vaccine in sufficient quantities and adequate uptake. For there to be reduced transmission of the virus there needs to be sufficient ‘herd immunity’ with most people immune to the disease either through a vaccine or people with antibodies from a previous infection, so fewer people contract and pass on the disease, preventing outbreaks. There are two main issues - current understanding is that just because someone has antibodies to COVID from a previous infection does not mean they can’t become reinfected. A possibility is that they may have suboptimal amounts of antibodies. For a vaccine, this may mean multiple doses are needed. Secondly, in a global world full of travel, we need global vaccine uptake. This may be difficult for low-income countries.

On a brighter note, it is thought that the genetic code of the coronavirus causing COVID-19 does not have a particularly high mutation rate. Mutations are few especially when compared to influenza and may not affect the severity of the disease much. This may mean that we need fewer vaccine jabs to have adequate protection.

Examples of COVID-19 vaccines

AZD1222 developed by the University of Oxford and AstraZeneca is showing some promise. It is currently in phase II-III of clinical trials meaning it is being tested for efficacy and safety in a large cohort of patients. Studies on participants revealed different antibodies by day 28 and day 56 suggesting it can elicit a useful immune response. It is a weakened version of the common cold virus with SARS-CoV-2 coronavirus genetic material (for a surface protein) added inside.

Another is mRNA-1273 developed in the US. This vaccine has reached phase III featuring 30,000 participants. Antibody production was found to be dose-dependent and responses were seen on a two-dose schedule. It has lipid nanoparticles that contain mRNA.

China has developed Ad50-CoV akin to AZD1222. It uses a common cold virus that can’t multiply in human cells with the genes of SARS-CoV-2 needed to make a surface protein. Antibodies and T cells (a class of cells involved in the immune response) were found at 14 days. This candidate vaccine has reached phase II which involves smaller numbers of patients.

Summary

Scientists and doctors across the globe are working hard on developing a vaccine against COVID-19. Prevention is better than cure so finding a non-toxic, effective vaccine remains a top priority. Numerous candidate vaccines are being trialled but it is likely only a minority of these will be successful. A vaccine is hopefully coming by early 2021. Treatments are also being researched.