We are in the middle of 2021st but the pandemic situation is not over yet. We are still living and adapting to all changes it brought. Every day people are infecting or dying because of Covid-19.
We’ve been under lockdown several times. Some people keep working from home until others decide to vaccine themselves. But are we all really familiar with the existing vaccines and those that are in the developing process?
Scientists make those kinds of vaccines by using genetically modified viruses (the vector). They are using the host translational machinery to express the foreign antigens. For example, vesicular stomatitis virus (VSV), lentivirus, influenza viruses, measles, and adenovirus vectors are using vector designs when it comes to vaccine development. Viral vector vaccines can be widely classified into non-replicating viral vectors and replicating vector vaccines.
A huge spectrum of viral vectors is subject to vaccine studies and vaccine development against Covid-19, especially in preclinical studies in animal models and in clinical trials. For example – there are 162 preclinical studies at the moment, 35 of them are based on VLPs or viral vectors.
Adenovirus-based vectors are the most preferred approach. This is because it is provoking sturdy antibody responses and protection against SARS-CoV-2 challenges in both rodents and primates.
Furthermore, protection is achieved after rodents’ immunization with LV, MVA, NDV, and VSV vectors. The classic delivery route comprises intramuscular administration, but also intranasal sprays have shown good results for adenovirus, LV, and influenza virus vectors.
Vaccines based on viral vectors are different from most standard vaccines – the difference comes from that they don’t contain antigens. They use the cells in our bodies to produce them.
It is happening by using a modified virus (that’s the vector) to convey genetic code for antigen, in the case of Coronavirus spike proteins discovered on the surface of the virus, into human cells. The cells are producing large amounts of antigen when they are infected. This triggers an immune response. The vaccine mimics the process during natural infection with defined pathogens, especially viruses. This gives the advantage of waking a powerful cellular immune response by T cells and the production of antibodies by B cells.
So far most other viral vectors have reached an only phase I, but several adenovirus-based vaccine candidates have successfully passed through phase I and II clinical studies. And the most advanced vaccine candidates are already classified in tens of thousands of volunteers.
Author: Donka Staykova