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  • Terry Clayton

How the Pfizer Vaccine Works

Updated: Dec 29, 2020


Everyone is now on the edge of their seats waiting. But for what exactly? How does the Pfizer vaccine #Covid19Vaccine, BNT162b2, actually work?


For comparison, here is how a typical flu vaccine is developed:

  1. Attenuated virus vaccine

  • A virus is forced to grow in different cell tissue (ex. Chick embryonic cells)

  • The virus is replicated and Isolated 80 + times (virus passaging)

  • As virus replicates over and over it adapts to the chick embryonic cells

  • Adaptation to chicken tissue results in a loss in potency (attenuation) in human tissue

  • When this now attenuated virus vaccine is given to humans, it struggles to replicate but still teaches the immune system how to produce antibodies

  • Vaccinated individuals build immunity but do not get sick or become contagious


2. Inactivated virus Vaccines

  • Live (or virulent) virus is cultured in tissue medium

  • Virus is killed using heat, chemicals or radiation and is harvested

  • The dead virus cannot replicate in host to cause infection or become contagious

  • Human immune system however will recognize virus

  • Body will recognize pathogen and evoke immune response

  • Immune response to inactivated virus is weak compared to attenuated virus and boosters may be required to build proper immunity

3. Pfizer's mRNA Vaccine

Now, lets talk about the Pfizer Covid-19 vaccine. Unlike the flu virus vaccine which is essentially a whole virus, the Pfizer vaccine is based on a part of the Covid virus called messenger RNA (mRNA).


Quick refresher on biochemistry:

DNA is use to transcribe mRNA. Proteins are created from mRNA through translation.



Eli Lilly has just received FDA approval for Emergency use of its new monoclonal antibody vaccine. You can read more about that here.


With mRNA vaccines, you are vaccinated with "pieces" of the virus. Specifically, pieces of the virus which encode for viral proteins. When the mRNA vaccine enters your cells, ribosomes locate it and use it to produce viral proteins (antigens). These proteins are harmless by themselves and will not cause infection. However, the presence of these proteins are perceived as a threat and B lymphocytes will respond by producing antibodies, an immune response. So now your body has created antibodies for the virus without having to experience infection.


You will find deeper look at how antibodies interact with the Spike (S) protein and the cells ACE2 protein here.


If you are subsequently infected with the covid virus, a memory B cell will quickly "remember" the antigen and produce antibodies against it. Put simply, these antibodies bind to the virus antigens and alert T lymphocytes to kill it. For a deeper dive on the immune response to covid read Chowdhury et al.


What this all means for you is simple: The vaccine teaches your body to identify and kill the virus quickly if detected. Today Pfizer has reported that their vaccine is more than 90% effective.


And that makes this family happy!



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