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Covid-19: 3 Things You Should Know About Pfizer's Vaccine

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The announcement of a 90% effective vaccine candidate against the Sars-CoV-2 coronavirus has caused panic in financial markets and raised hopes and questions. We provide you with three main facts that you should know about this vaccine developed by Pfizer.

While these initial results (90% effectiveness) are very encouraging, it is important to remember that testing for this vaccine candidate is not yet complete.

In its press release of November 9, the giant Pfizer indicates that the recruitment of volunteers for this phase 3 clinical trial, which began on July 27, is still ongoing. They should continue until the final analysis when a total of 164 confirmed cases of Covid-19 have accumulated. So far, only 94 people have been infected with Sars-CoV-2, out of about 43,538 participants. Therefore, while this is obviously not desirable, the rate of effectiveness may not be as high as expected. Pfizer itself specifies that "when the study is in progress, the final efficacy percentage of the vaccine may vary." That said, the Food and Drug Administration (FDA), the US pharmaceutical agency, has warned that it will give the green light to commercialize a vaccine if it shows an efficiency of more than 50%.

In a study published in mid-July in the American Journal of Preventive Medicine, researchers estimated that to end the current pandemic, the vaccine would need 60% efficacy if 100% of the population is vaccinated (we are talking about coverage of vaccination). With less vaccination coverage, which is the scenario that seems to arise, the effectiveness of the vaccine will have to be even greater.

70% efficiency with 75% vaccination coverage

80% efficiency with 60% of the vaccinated population, when the reproduction rate (number of people infected by one patient, the famous Ro) is 2.5.

Also note that the only scientific data currently available on this candidate vaccine is the protocol and press release sent by Pfizer. The developed vaccine has not yet been published scientifically, but Pfizer and BioNTech plan to submit the data from the full Phase 3 trial for the scientific community to consider in a dedicated publication. The methodology followed is certainly important to validate the results obtained.

Note that China and Russia have already started vaccinating part of their population, and this while phase 3 trials of the candidate vaccines used have not yet been completed.

A vaccine based on a new approach

While all vaccines serve the same purpose, which is to make the immune system recognize and fight an infectious agent (virus or bacteria), they can be designed in different ways. They can consist of inactivated viruses (example: pertussis vaccine), or attenuated, that is, having lost its pathogenicity (as in the case of measles or tuberculosis). A vaccine can also be made up of antigens (proteins or others): then it is a fragment present on the surface of the virus, which will be recognized by antibodies and / or by cells of the immune system. Hepatitis B or human papillomavirus (HPV) vaccines.

Here, the technology used, called messenger RNA (mRNA), is innovative. We inject into the body a fragment of genetic instruction, which will enter our cells in order not to modify our DNA (unlike some fake news that circulate) but to manufacture a protein present on the surface of the coronavirus, here protein S or protein Spike. Which will then be detected by our immune cells, resulting in an immune response. Our cells become like transitory factories to produce a virus membrane protein. Only protein S will be created on the surface of the virus, and this is a priori harmless on its own.

Note that no mRNA or DNA vaccine has been approved for humans yet. In contrast, DNA vaccines are used for veterinary use.

Hope for the creation of vaccines against other diseases

If this vaccine approach is validated and confirmed to be effective, it could pave the way for the implementation of other vaccines that also use mRNA. To name just one laboratory in the niche, Moderna is working, for example, on the development of mRNA vaccines against Zika virus, against Chikungunya, against Epstein-Barr virus (responsible for mononucleosis), against cytomegalovirus. (or CMV), against certain cancers or against the influenza virus. She is also developing an mRNA vaccine candidate against Sars-CoV-2.

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