By Dr Leow Chiuan Yee
The key function of a vaccine is to offer protection to an individual by triggering the immune response against the infected disease. In the current COVID-19 vaccines, as of today, there are four categories of vaccines which have completed or in the final stage of the clinical trials.
The types of the vaccine include whole virus, protein subunit, viral vector and nucleic acid (RNA AND DNA). Ad5-nCoV, developed by CanSino Biologics and an arm of the People’s Liberation Army, was the first candidate to enter human trials and is currently in clinical phase 3. It is a viral vector vaccine and uses non-replicating adenovirus type 5 vector, to transport the DNA of spike proteins of SARS-CoV-2.
The concept is to transform the spike proteins within the body, ultimately leading to the activation of the immune system. Using the same technology, researchers from Oxford University and AstraZeneca developed ChAdOx1, which will eventually produce spike proteins within the human body, leading to immune system activation.
ChAdOx1 has already completed phase 3 clinical trials, an acceptable safety profile and 60 – 90% vaccine efficacy. CoronaVac, currently in phase 3 trial, is an inactivated vaccine developed by Sinovac, a Chinese private biopharma company, based on the traditional fact that exposure to an inactivated virus will eventually lead up to the immune response.
The Beijing Institute of Biological Products/Wuhan Institute of Biological Products is working on few inactivated vaccines, which are in the clinical phase 3. However, they are relatively unadvertised outside Chinese media.
Besides this, two RNA vaccines have been approved, named as mRNA-1273 by US biotech firm Moderna/NIAID and BNT-162 jointly by German company BioNTech and US pharma giant Pfizer. Both these vaccines follow the concept of delivering information molecules to instruct human body cells to produce the spike proteins of SARS-CoV-2.
This information molecule is mRNA in the case of BNT-162, whereas LNP-encapsulated mRNA in mRNA-1273. Russia’s Sputnik V coronavirus vaccine developed by Gamaleya Research Institute, has recently published its phase 3 clinical trial data in the Lancet. The vaccine gives around 92% protection against Covid-19.
It has also been revealed to be safe – and offer complete protection against hospitalisation and death. Although the vaccine is based on adenoviral vector technology, unlike Oxford-AstraZeneca, this vaccine uses two different viral vectors.
Changing the vector for the second dose decreases the risk of potential immune response to the vector itself from reducing the efficacy of the overall vaccine.
Dr Leow Chiuan Yee is a Senior Lecturer at the School of Pharmaceuticals Science, University Sains Malaysia and YSN-ASM affiliate.
**All previous posts about COVID-19 here: https://sciencemediacentremalaysia.com/tag/covid-19/