Scientists are working around the clock to develop and test a vaccine against SARS-CoV-2, the agent that causes Covid-19. Experts agree that widespread use of a safe and effective vaccine will quickly contain the Covid-19 pandemic, preventing transmission and disease.
A key step in any vaccine development process is clinical testing, which involves administering a vaccine or placebo to a human subject, then evaluating its health effects over a period of time. These tests help demonstrate safety in diverse human populations living in different settings, and to determine vaccine efficacy – the ability to prevent infection and disease.
Globally, Covid-19 vaccine trials are being carried out on all continents, representing all of the world’s diverse human populations. In Africa, Egypt and South Africa participated in this trial. Many other countries are also preparing to participate.
To date, there are 260 Covid-19 vaccine candidates at various stages of development. Sixty of them are currently undergoing clinical trials (human trials) in different phases. This includes phase III trials – the point at which scientists aim to determine how well a vaccine protects (efficacy) trial participants from infection or severe Covid-19 symptoms.
November 2020 has become a month of celebration. Preliminary stage III data from three different Covid-19 vaccine candidates show very high efficacy ranging from 70% to 95%. All three – the Pfizer / BioNTech, Moderna mRNA-1273 and Oxford ChAdOx1-S vaccines – are in the final stages of phase III clinical trials. Pfizer / BioNTech and Oxford ChAdOx1-S are being tested in Africa as well. After investigating the initial safety concerns in the Phase III trial, testing of the Oxford ChAdOx1-S vaccine has been going well.
Innovative developments offer hope and optimism. However, there are still big obstacles ahead, especially for developing countries. Main among these is the fact that at least one of the promising vaccines needs to be stored at very low temperatures before use. This will be a difficult request for most African countries.
Additionally, there are concerns about access to vaccines once production has started. Among the main concerns is the availability of sufficient vaccine doses to meet the high demand. And then there’s the question of affordability. Resources will be needed to quickly procure and distribute the Covid-19 vaccine.
Much focus is placed on the COVAX Facility, a global risk-sharing plan co-led by GAVI. It oversees the gathering of the procurement and fair distribution of the Covid-19 vaccine.
There are three vaccines in stage III with a similar choice of antigen – the SARS-CoV-2 spike protein. But they work differently in the way they teach the immune system to protect our bodies from Covid-19.
Pfizer / BioNTech is an mRNA vaccine. Such vaccines work by instructing human cells to make a fraction of a viral surface protein and inducing the appropriate type of immune response thought to provide protection. In this case, it’s an immune response to the spike protein SARS-CoV-2. This protein plays a key role in allowing the coronavirus to infect human cells and replicate.
In some people who are infected, Covid-19 progresses, while others remain asymptomatic, without any signs or symptoms of the disease. Initial data indicate no major safety concerns associated with administering two doses of the vaccine. This mRNA-based Covid-19 vaccine induces a strong neutralizing antibody immune response and T-cells. T-cell and antibody immune responses are thought to be important in protecting against Covid-19. A similar mRNA vaccine, made by Moderna, shows comparable results.
95% efficacy has been reported for the Pfizer / BioNTech (mRNA) vaccine, far exceeding expectations. This type of vaccine can be rapidly produced and upgraded to meet the high demand for millions of doses. If licensed, it will be the first mRNA vaccine approved for human use by regulatory authorities.
Oxford ChAdOx1-S is a non-replicating viral vector vaccine. The viral vector, or backbone, used in this vaccine is based on the chimpanzee adenovirus (ChAd). The choice of this vector type is to circumvent pre-existing common immunity to human adenovirus (HAdV) which would blunt the ability of such a vaccine to engage the human immune system.
Scientists are experienced with clinical trials (safety and immunological profiles) of the ChAd virus vector vaccine.
Oxford ChAdOx1-S works by using a replicating deficient adenovirus vector to easily deliver spike proteins to immune cells or tissues, thereby inducing the desired immune response against SARS-CoV-2. Vaccine-induced immunity consists of T-cells and a strong neutralizing antibody (inhibiting infection) immune response.
Novavax NVX-CoV2373 is a protein subunit vaccine. Subunit vaccines work by presenting specific antigens that stimulate the immune system to increase its response. Importantly, this type of vaccine requires combination with adjuvants (compounds that enhance the immune response), because antigens alone are not sufficient to induce optimal long-term immunity.
The antigen (spike protein) in the NVX-CoV2373 vaccine is prepared and purified from cell culture, then formulated – together with the Novavax saponin-based Matrix-M adjuvant – into nanoparticles. There is extensive clinical experience of this type of vaccine platform in terms of safety and immunogenicity, such as the seasonal influenza vaccine.
Initial data suggest NVX-CoV2373 vaccine-induced immunity is composed of T-cells and a strong neutralizing antibody immune response. It is likely that this two-dose schedule vaccine candidate will show high efficacy.
The big challenge for the Pfizer / BioNTec vaccine is the cold chain requirement. It needs to be transported and stored at very low temperatures (-70 ° C, on dry ice) before use. Immunization programs – especially those on the continent – do not yet have the vaccine supply and cold chain infrastructure that can handle this vaccine optimally. This is especially true in tier one health care facilities where immunizations are routine.
This means that significant investment must be made before it is rolled out to communities in remote areas. This could cause massive delays in vaccine use, especially in low and middle income countries. The good news is that innovative approaches, such as the design and development of suitable transport containers, can overcome these challenges.
The other two vaccines can be handled within the current immunization cold chain infrastructure that maintains temperatures in the range of 2 ° C to 8 ° C prior to use.
Another potential challenge is that the use of one of these vaccines by national immunization programs needs to be informed by timely, high-quality evidence that takes into account the local context. This means national policymakers must immediately and carefully weigh the benefits and drawbacks of individual vaccines before deciding which one to use.
Regarding fees and access, a lot of effort was put into the COVAX Facility. This appears to be the only insurance policy in Africa not to be the last in the queue.
Benjamin Kagina, Senior Research Officer, Vaccine Initiative For Africa, Faculty of Health Sciences, University of Cape Town
This article is republished from The Conversation under a Creative Commons license. Read the original article.