UK’s Medicines and Healthcare Regulatory Authority ( MHRA) and the USA’S Food and Drug Administration ( FDA) have granted emergency use authorization( EUA) to COVID-19 vaccine, manufactured by USA based pharmaceutical Co. Pfizer in tie-up with Germany based biotechnology company BioNTec. Both UK and USA have started vaccinating their citizens with this mRNA based vaccine known as BNT 162b2 which was found to be 95 per cent effective against SARS-COV-2( COVID-19 causing Coronavirus) according to early phase 3 clinical trial data. According to Pfizer, no serious safety concerns were reported in a study of 43,538 trial participants, 42 per cent of whom belonged to diverse racial or ethnic groups of 6 different countries.
The data provided by Moderna, USA and AstraZeneca– Oxford University, UK are being analyzed by Regulators in the USA and European Union for the purpose of granting EUA. The vaccines are known as mRNA 1274 and AZD1222 of Moderna and AstraZeneca respectively have also been tested in large clinical trials and have been reported to be safe (Moderna’s mRNA— 95 % safe and AstraZeneca-Oxford’ s AZD 1222— 70 % safe) and efficacious and are expected to get the nod for conducting emergency trials in due course of time. Finally, at the end of the year 2020, three Coronavirus vaccine manufacturing companies namely Pfizer- BioNTec, Moderna and AstraZeneca-Oxford University are front-runners in the global race to contain a raging pandemic. All the 3 vaccines are given in two doses 3-4 weeks apart. Pfizer has also applied to Drugs Controller General of India ( DCGI) for EUA. The applications of Pune based Indian Institute of Serum which is the Indian collaborator of Astrazenica- Oxford, UK and indigenous Bharat Biotech for EUA have not been cleared as yet. Both Pfizer’s and Moderna’s vaccines are mRNA ( messenger Ribonucleic Acid) based, mRNA vaccine technology is novel and mRNA vaccines before this have not been licensed to vaccinate the population.
In our cells, the information to synthesize proteins is present in genetic material known as Deoxyribose Nucleic Acid ( DNA) which forms mRNA containing the templates for making proteins. The mRNA then reaches to biological machinery where this information is read to translate it into protein formation. Pfizer’s and Moderna’s mRNA vaccines contain the information for producing spike protein of Coronavirus SARS-COV-2 that causes COVID-19. The spike proteins are present on the surface of the virus and interact with human cells to infecting them. The spike proteins after being synthesized by mRNA vaccine are recognized by the human immune system as an antigen which serves as a signal to activate the immune system. The activated immune system produces the memory B cells and T cells in large numbers. Subsequently on an actual encounter with Coronavirus, the memory B-cells and T-cells produced after vaccination interact with antigen i.e spike protein of the Coronavirus. The B cells produce antibodies which kill the virus when it is outside the human cells. When the virus enters into our cells e.g. lungs cells, these cells harbouring the virus ( intracellular) are killed by activated cytotoxic T cells. One type of T-cells known as T- helper cells helps the B-cells and T-cells to perform their respective jobs by providing them chemicals known as cytokines. AstraZeneca– Oxford University’s vaccine AZD 1222 is a genetically engineered adenovirus vaccine in which harmless, non-replicable adenovirus contains genetic material i.e. DNA that encodes for Coronavirus spike protein.
The efforts of the scientists to develop and test the three vaccines for COVID- 19 described in this article in such a short timeframe since the Coronavirus ( SARS CoV-2 ) emerged in the month of December 2019 in Wuhan, China, are certainly great achievements and deserve to be complimented. But following queries need to be addressed. Although all the 3 frontrunner vaccines described above have passed safety and efficacy tests in large clinical trials and one of them i.e Pfizer’s BNT 162 b2 has been granted emergency use authorization ( EUA) under which USA and UK citizens are being immunized by using this vaccine, there are no clinical trial reports which show that they really reduce the viral infection or reduce the spread of virus completely in a population.
In other words, it means that there is a chance of vaccinated individuals remaining susceptible to asymptomatic infection who then are capable of transmitting that infection to other vulnerable people. According to Professor Jonathan Ball of Molecular Virology, School of Life Sciences in University of Nottingham, England, a truly effective vaccine is the one which protects those most vulnerable from becoming infected and then transmitting the virus to others. Simply reducing the appearance of symptoms in people who would otherwise have experienced mild infection is unlikely to have a major benefit.
The clinical trial reports of three vaccines also do not indicate how long vaccine-induced immunity to SARS-COV-2 virus will last. Hopefully, the final clinical trial reports of the vaccines will have the answer to these queries!
By Dr Aqueel Khan
Professor & Head ( Retd.)
University Postgraduate Teaching Department of Biochemistry,
RTM Nagpur University, Nagpur, Maharashtra