SARS-CoV-2 is a single-stranded RNA-enveloped virus. As the epidemic spreads, it is critical to find a specific therapeutic for COVID-19, and vaccines targeting various SARS-CoV-2 proteins are under development. Conversely, the other three, SARS-CoV, MERS-CoV, and SARS-CoV-2, are able to cause severe symptoms and even death, with fatality rates of 10%, 37%, and 5%, respectively.Īlthough a large number of studies and clinical trials are being launched on COVID-19 around the world, no evidence from randomized clinical trials has shown that any potential therapy improves outcomes in patients. It is the seventh known coronavirus to infect humans four of these coronaviruses (229E, NL63, OC43, and HKU1) only cause slight symptoms of the common cold. The COVID-19 was quickly discovered to be caused by a coronavirus later named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which belongs to the β coronavirus family. Extensive testing is therefore required after every step, increasing costs.The epidemic of novel coronavirus disease 2019 (COVID-19) was caused by a new coronavirus occurred in December 2019, and now has spread worldwide and turned into a global pandemic. Assembling the vector vaccine is also a complex process, involving multiple steps and components, each of which increases the risk of contamination. Suspension cell lines are now being developed, which would enable viral vectors to be grown in large bioreactors. Traditionally, viral vectors are grown in cells that are attached to a substrate, rather than in free-floating cells - but this is difficult to do on a large scale. How easy are they to manufacture?Ī major bottleneck for viral vector vaccine production is scalability. Such “anti-vector immunity” also makes delivering a second dose of the vaccine challenging, assuming this is needed, unless this second dose is delivered using a different virus vector. One challenge of this approach is that people may previously have been exposed to the virus vector and raise an immune response against it, reducing the effectiveness of the vaccine. They have been trained to recognise the body’s own proteins as ‘self’, so if they notice a foreign protein, such as an antigen from the pathogen, they will mount an immune response against the cell carrying it. T cells do this by examining the repertoire of proteins expressed on the surfaces of cells. This response includes antibody-producing B cells, as well as T cells, which seek out and destroy infected cells. When the immune cells detect the foreign antigen, they mount an immune response against it. Human cells manufacture the antigen as if it were one of their own proteins and this is presented on their surface alongside many other proteins. Once injected into the body, these vaccine viruses begin infecting our cells and inserting their genetic material – including the antigen gene – into the cells’ nuclei. The COVID-19 viral vector vaccines under development use non-replicating viral vectors. Replicating vector vaccines also produce new viral particles in the cells they infect, which then go on to infect new cells that will also make the vaccine antigen. Non-replicating vector vaccines are unable to make new viral particles they only produce the vaccine antigen. There are two main types of viral vector-based vaccines. ![]() The genetic instructions for making the antigen from the target pathogen are stitched into the virus vector’s genome. Various viruses have been developed as vectors, including adenovirus (a cause of the common cold), measles virus and vaccinia virus. These vectors are stripped of any disease-causing genes and sometimes also genes that can enable them to replicate, meaning they are now harmless. The virus itself is harmless, and by getting the cells only to produce antigens the body can mount an immune response safely, without developing disease. The viral vector acts as a delivery system, providing a means to invade the cell and insert the code for a different virus’ antigens (the pathogen you’re trying to vaccinate against). A similar principle underpins viral vector vaccines - only in this case, the host cells only receive code to make antigens. These virus particles contain antigens, molecules that can trigger an immune response. Viruses survive and replicate by invading their host’s cells and hijacking their protein-making machinery, so it reads the virus’ genetic code and makes new viruses. Relatively complex to manufacture How do such vaccines trigger immunity?
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