Sunday, December 20, 2020

The BNT162b2 Covid-19 Vaccine: Pfizer-BioNTech Vaccine


The BNT162b2 mRNA Covid-19 vaccine, popularly known as the Pfizer vaccine is the first Covid-19 vaccine to receive authorization for use in the general public. The first jab was given to a 90-year old lady in the UK on December 8, 2020; a monumental event that brought hope to billions of people all across the globe. In this article, I will discuss this vaccine’s clinical trial and potential future implications.


How does it act?

The BNT162B2 is a lipid nanoparticle-formulated, nucleoside-modified mRNA that encodes the SARS-CoV-2 full-length spike protein, modified by two proline mutations to lock it in the prefusion conformation. This means that this is an mRNA that has been modified to resist disintegration by nucleases and that translates into the SARS-CoV-2 spike protein. However, this spike protein has also been modified to lock it into its pre-fusion conformation; so that it doesn’t fuse with the target cell’s plasma membrane and remain exposed to immunogenic stimulation.


Who is it for?

This primarily depends on the characteristics of the population included in the vaccine’s clinical trial. This trial randomised 43,458 persons from six countries: USA, Argentina, Brazil, South Africa, Germany, and Turkey. More than three-fourth of the study population (76.7%) belonged to the USA. Moving on to the representation of race or ethnicity in the study population - 82.9% were white, 27.9% were Hispanic, while African Americans, Asians, and Native Americans comprised 9.2%, 4.2%, and 0.5% of the study group. Males and females were almost equally included. The age range is from 16 years to 89 years in the intervention group. This trial did not evaluate the efficacy of the vaccine in children, adolescents, and pregnant women.  


Is it effective?

Define effective; it depends on the trial’s efficacy end points. The primary endpoint was the efficacy of the vaccine to prevent Covid-19 infection 7 days after the second dose in participants who had no serologic (antigen and antibodies) or virologic (RT-PCR) evidence of SARS-CoV-2 infection up to 7 days after the second dose; the second primary endpoint was to prevent infection in those with and without evidence of prior infection. Confirmed Covid-19 was defined as – the presence of at least one symptom (fever, new or worsened cough, new or worsened dyspnoea, chills, new or worsened muscle pain, new loss of taste or smell, sore throat, diarrhoea or vomiting combined with a positive RT-PCR test within 4 days).    



Efficacy End Point


BNT162b2 Group


Placebo Group

Vaccine efficacy, % (95% credible interval)

Covid-19 Cases


Covid-19 Cases


1st Primary






2nd Primary






 This trial showed that a two-dose regimen of BNT162b2 (30 micrograms per dose, given 21 days apart) was 95% effective in preventing symptomatic Covid-19 infection 7 days after its course. The efficacy was 52% after the first dose, and 91% in the first 7 days after the second dose.

However, the trial results did not show the efficacy in preventing asymptomatic infection. We don’t know if this vaccine can safeguard against transmissible asymptomatic infection; therefore, people who have taken the vaccine should not stop wearing masks for the sake of the people around them.


Is it safe?

The vaccine group reported more local reactions, such as pain, redness, and swelling at the injection site than the placebo group. In general, these were mild-to-moderate in severity and resolved within 1-2 days. The systemic adverse effects were also reported more in the intervention group, especially in the younger population (16 to 55 years of age), and more after the second dose. These included – fever (11%), fatigue (51%), headache (39%), chills (23%), muscle pain (29%), joint pain (19%), and 38% of the vaccine group needed to use antipyretic medication. These were generally mild and resolved within 1-2 days. Two deaths happened in the vaccine group, one from arteriosclerosis, and one from cardiac arrest. These deaths weren’t related to the vaccine or Covid-19. The investigators plan to continue the surveillance for adverse events for further 2 years.  


This study has importance beyond the efficacy of the BNT162b2 vaccine candidate. It demonstrates the utility of RNA-based vaccines, its speed of development, and its promising efficacy in preventing infectious diseases. The success of this clinical trial immensely improves our preparedness for a future pandemic.


Polack, FP, et al. Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine. New England Journal of Medicine. Dec 10, 2020. 10.1056/NEJMoa2034577. C4591001 Clinical Trial group


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