Introduction:  Last week, the world received positive news about the Pfizer vaccine. The preliminary results suggested their vaccine was more than 90% effective against COVID-19 [1]. But, how does the vaccine work? The Pfizer and BioNTech vaccine (BNT162b2) is composed of nucleoside-modified messenger RNA (modRNA) and encapsulated in lipid nanoparticles.This works by stimulating our own cells to make a viral protein, unlike traditional vaccines. When these viral proteins are encountered with our immune system, antibodies are made.This enables our immune system to recognise the virus and attack it. mRNA, which is a molecule that contains instructions to make proteins, is injected and causes the cells to produce a glycoprotein called “spike”. Glycoproteins are groups of proteins that contains carbohydrate groups attached to the polypeptide chain.The spike glycoprotein is found in the outer envelope of coronaviruses, as shown in Fig.1. Its function is to recognise and interact with other cells.Research has shown that 2019-nCov can infect human respiratory epithelial cells through interaction of the spike glycoprotein with human ACE2 receptors, allowing the virus to get entry into those cells [2].

A huge advantage of the mRNA vaccine is that scientists can save time by skipping the laboratory production of the proteins. mRNA is a partial copy of DNA involved in making proteins.Therefore,by directly injecting the molecular instructions to make the protein into the human body itself, the difficult manufacturing and purifying process of proteins is avoided [3].This enables mimicry of the antigen structure and expression as seen in the course of a natural infection [4].

Clinical trials summary: During the clinical trial of 2 different RNA vaccine candidates, three factors were assessed: reactogenicity (ability to produce common, adverse reactions), immunogenicity (ability to provoke an immune response), and safety.This clinical trial was taken place in 3 phases and was a randomised, placebo -controlled, observer-blind, dose-finding, vaccine candidate-selection, and efficacy study in healthy individuals. Approximately 44,000 participants took part in the study across three age groups (12-15, 16-55 or >55 years of age) and were tested at varying dosage levels. 42% of the global participants had racially and ethnically diverse backgrounds.This is an important consideration, since ethnic minorities have been adversely affected by COVID-19.It was found that the effective dosage was the 30 µg dose level in a 2 dose schedule (separated by 21 days) at the mid-dose level-BNT162b2 [5][6].The results indicated an efficacy rate above 90% at 7 days after the 2nddosage.

Limitations and Side effects:  There are few limitations in this study:since the mRNA vaccine is a relatively novel technology, it requires extensive testing for the safety and efficacy of a vaccine. During the clinical trials mostly mild side effects were recorded by the volunteers. This included injection site pain, fatigue, headache, chills, muscle pain, and joint pain.A possible logistical problem is that BNT162b2 requires storage at  –80°C [7]. Since mRNA is very unstable, storing it at this temperature prevents it from breaking down.This poses a great challenge for worldwide transport, distribution and storage of the vaccine. In order to reach high efficacy, 2 doses are needed within a 21 day interval.This means that the production of twice as many doses is needed and so clinics would need to keep track and readminister the vaccine appropriately.

Conclusion:  The need of the hour is to develop a safe and effective COVID-19 to terminate this pandemic.Although the Pfizer vaccine has shown promising results in the clinical trials, it is important to note that there will not be a single vaccine winner; different strengths are offered by other vaccines, especially in distinct epidemiological contexts. Additionally, a single vaccine will be insufficient supply in the initial stages [4].

© COPYRIGHT: This article is the property of We Speak Science, a non-profit institution co-founded by Dr. Detina Zalli and Dr. Argita Zalli. The article is written by Shanthavi Wijayakumar, King’s College London, UK.


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