All you wanted to know about mRNA vaccines

India will soon have a mRNA-based vaccine from US-based biotech firm, Moderna Inc, joining the fight against Covid-19. The mRNA vaccine is a new kind of vaccine that adds to the existing choices of non-replicating vector vaccines such as Covishield (Serum India) and Sputnik V (Russian-based Gamaleya Institute) and the inactivated pathogen based Covaxin (Bharat Biotech).

The human immune system is usually slow to identify and target a fast-replicating virus like Covid-19. Vaccines introduce the target to the immune system beforehand and get it geared up, well before an actual virus enters the body. Traditional vaccines use dead or weakened viruses to train the immune cells. Messenger Ribonucleic Acid or mRNA based vaccines are encoded with target virus’s genetic information. They carry these instructions to the body that then develops the spike protein, while leaving out harmful parts of the virus. Active immune cells identify this spike protein and begin the process of making antibodies for the spike. They also store vital information for the future. When the actual coronavirus with the spike enters the body, the immune system is alert and ready to attack it. The spike protein essential to this process is unique to SARS-CoV-2, eliminating the risk of autoimmune reaction on healthy cells.

mRNA based treatment started in mid-90’s and was nearly abandoned due to lower stability, quick trigger of an immune reaction and inefficient delivery. mRNA research lately has overcome these limitations and proved to have additional benefits over traditional vaccines. mRNA vaccines can be made and developed rapidly which is why vaccines of Moderna Inc and BioNTech/Pfizer were among the earliest to reach the highly regulated markets in the West. mRNA vaccines allow for a high degree of modulation including addressing cancer treatments. They are non-infectious causing lower side effects.

Of the nearly 300 vaccines in pre-clinical and clinical development, 38 per cent are based on traditional non-replicating viral vector and 24 per cent are from inactivated virus. Thirty-eight per cent are based on mRNA. In the mRNA space itself, Moderna’s vaccine is amongst the three with large scale Phase 3 trials conducted and with reported efficacy rate of 94.1 per cent.

India’s vaccination programme so far has relied mainly on Covishield and Covaxin which are not mRNA vaccines. However, after a brief tussle on matters of indemnity, Moderna’s mRNA vaccine has got an emergency use authorization from DCGI last month. With Moderna paving the way, even BioNTech/Pfizer’s vaccine could follow suit. Knowing how the different vaccines work can help you make an informed choice on the type of vaccine. mRNA vaccines are also under consideration for inoculating children.

Herd immunity, which is vital to beat the pandemic, is reached when 60-70 per cent of the population acquires immunity, nullifying the node-based spread of the virus specific to Covid-19. Slow replicating H1N1 influenza requires a herd immunity of 25-37 per cent while measles and chickenpox required more than 90 per cent immunity levels. India should target vaccinating 94 crore adults who are 18 years of age and above with two doses. Till July 12, 2021, India has completed just 37.7 crore vaccinations with two doses for 7 crore people, essentially relying upon Covishield and Covaxin. The Centre’s target of 186 crore doses by year end may need mRNA vaccines to enter the picture.

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