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Difference Between AstraZeneca and Pfizer

It’s been almost a year since a terrifying science fiction tale suddenly became our worst nightmare and this pandemic is still far from being over. We are still in the middle of this unexpected pandemic and no one knows how bad this will get or how long it will last. Like everybody, we are optimistic that science will come to our rescue, and for the time being, our only hope of bringing this virus under control, now lies with the scientists and the vaccines developed by them. However, with so many vaccine candidates out there, it is getting a bit difficult to pick the right one, at least for people like us who do not know the science behind these vaccines. Two such COVID-19 vaccines that are approved for emergency use are AstraZeneca and Pfizer. 

What is AstraZeneca vaccine? 

Although, the use of AstraZeneca has been halted in a number of European countries following the adverse effects of the vaccine including blood clotting that raised some serious concerns among, the UK’s medical regulator still says it’s completely safe to use. The reports of certain patients developing blood clots after taking the jab came to light, as a result of which Germany, Italy, and France among other countries have put a stop on the vaccination drive as a precautionary measure.  

AstraZeneca, codenamed AZD1222 is a COVID-19 vaccine developed by the University of Oxford and produced locally by the Serum Institute of India (SII) – one of the largest manufacturer of vaccines in the world. It is among the few chosen vaccine candidates to be approved for mass inoculation, along with Pfizer, Moderna and Johnson & Johnson’s COVID-19 vaccine. The AstraZeneca vaccine contains a dead virus known as the adenovirus, which is basically the weakened version of a common cold virus that causes infections in chimpanzees. So, this virus carries a small bit of the genetic code of the SARS-CoV-2 virus spike protein. After the vaccine in injected, the surface spike protein is produced, which preps the immune system to attack the SARS-CoV-2 virus.

What is Pfizer vaccine?

The Pfizer BioNTech COVID-19 vaccine is a mRNA-based vaccine developed by the American pharmaceutical giant Pfizer in collaboration with their German partner BioNTech. The mRNA or messenger RNA is a cutting-edge technology to develop vaccines in masses and much faster compared to other vaccine methods. This vaccine candidate is not made with the actual COVID-19 virus; in fact, it’s made with the genetic material for a spike protein that is attached to the surface of the COVID-19 virus. The virus creates copies of the virus by attaching its spikes to the host cell. Those spikes are a potential target for vaccines.

The Pfizer vaccine contains that genetic material, called mRNA and when it is injected, it preps our immune system by directing cells to make specific proteins, which are harmless and which directs our immune system to quickly detect a coronavirus infection if any and produce the appropriate antibodies. So, the new antibodies respond when it detects the coronavirus infection and attach themselves to the COVID-19 spikes, rendering the spikes harmless, protecting our cells, and preventing the reproduction of the virus. The vaccine demonstrated promising results with a 90% efficacy rate in patients with no evidence of any prior COVID-19 infection.

Difference between AstraZeneca and Pfizer


– The Oxford University’s AstraZeneca COVID-19 vaccine is a Recombinant vaccine based on Viral Vector Technology which uses the weakened version of a common cold virus called the adenovirus that causes infections in chimpanzees. This virus carries a small bit of the genetic code of the SARS-CoV-2 virus spike protein, which when injected renders the virus useless, prepping the immune system to attack the SARS-CoV-2 virus. The Pfizer BioNTech vaccine, on the other hand, is mRNA-based vaccine made with the genetic material for a spike protein that is attached to the surface of the COVID-19 virus. When injected, it directs our immune system to quickly detect a coronavirus infection and produce the appropriate antibodies to fight off the virus.


– Based on the initial reports and the clinical trials data produced by the manufacturer, the AstraZeneca vaccine is believed to be 63% effective against the COVID-19 virus. A full fledge vaccine rollout has already started in the UK and the Vaccine Minister confirmed that almost a 15 million vulnerable people have already been vaccinated with the first doses till Feb 14, 2021. But many countries have temporarily suspended the use of the AstraZeneca vaccine because adverse effects of the vaccine on some patients who reported blood clotting problems after the dose. The Pfizer BioNTech vaccine is proved to be the most effective vaccine candidate against the COVID-19 virus with an efficacy rate of around 95%, which is very promising.

Storage & Dose 

– The AstraZeneca vaccine can be stored and transported at normal temperatures and they can be stored safely for up to 6 months between 36and 46 degrees Fahrenheit. As for dosage, the recommended dosage is two intramuscular injections (0.5 ml each) placed at 8 to 12 weeks apart. Like AstraZeneca, Pfizer vaccine is two-dose shots administered as intramuscular injections with 0.3 ml each and set 3 weeks apart. So, if the first dose is on Day 1, then the second dose is scheduled for Day 22. As for storage, the Pfizer vaccine must be stored at sub zero temperatures before they are ready to use.

AstraZeneca vs. Pfizer: Comparison Chart


While both AstraZeneca and Pfizer are among the top contenders in the ongoing COVID-19 vaccine race, the Pfizer vaccine is proved to be the most effective with an unmatched efficacy rate of almost 95% compared to AstraZeneca’s 63%. But the question is how effective they will be in preventing the COVID-19 infection on the long run and how fast the world population gets the vaccines. The reports of blood clots on some patients after the dose of AstraZeneca vaccine have already created a sense of chaos in the people, and as a result many countries have put a halt on the use of the AstraZeneca vaccine for now. But the pandemic is far from being over, so the vaccine war is still on.

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References :

[0]Foley, Katherine Ellen. “The Metric That Will Determine the Real Winner of the Covid-19 Vaccine Race.” Quartz, Quartz Media Inc., https://qz.com/1935017/moderna-vs-pfizer-who-will-win-the-covid-19-vaccine-race/. Accessed 21 Mar. 2021

[1]Romanowski, Victor. Current Issues in Molecular Virology: Viral Genetics and Biotechnological Applications. London, United Kingdom: Intech Open, 2013. Print

[2]Image credit: https://live.staticflickr.com/65535/50714715547_f8553552f9_b.jpg

[3]Image credit: https://commons.wikimedia.org/wiki/File:Oxford_AstraZeneca_COVID-19_vaccine_(2021)_I.jpg

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