Questions have been raised about the differences in vaccines after the National Advisory Committee on Immunization (NACI) recommended mRNA vaccines as “more recommended” than other viral vector-based vaccines in recommendations to combat the CCHV.
To date, Health Canada has currently licensed four different mRNA vaccines manufactured by Pfizer (Ffizer-BioNTech), Moderna, AstraZeneca (AZ) and Johnson & Johnson.
The Pfizer BioNTech and Moderna vaccines use mRNA technology, while the AZ and single-dose Johnson & Johnson vaccines are viral vector-based vaccines.
So what’s the difference between the mRNA vaccine and the viral vector vaccine? Why does the NACI recommend one over the other?
What is a viral vector-based vaccine?
Viral vector-based vaccines (e.g., AZ, the vaccine developed by Johnson & Johnson) use live harmless viruses or adenoviruses as delivery to trigger the immune system to produce antibodies against infection by the SARS-CoV-2 producing CCA virus.
The adenovirus is not SARS-CoV-2 itself, but rather an otherwise harmless virus that has been modified so that it cannot replicate in the body and cause disease.
Health Canada explains on its website that adenovirus is the virus that causes the common cold and that there are many different types that have been used for decades to provide the protein for vaccine production.
In the case of the CCA virus vaccine, the vector virus delivers specific genetic instructions to cells in the body to produce harmless SARS-CoV-2, called the spike-in protein. The cells then produce this stinger protein, which triggers an immune system response.
Subsequently, the immune system produces antibodies against this stinger protein to fight the disease it believes to be an infection. If the immune system subsequently encounters the real SARS-CoV-2 virus and its stinger protein, our body already has antibodies for defense.
Because the viral vector vaccine is genetically modified, it is unable to replicate, which means that once antibodies are produced, the viral vector previously injected into the body is completely eliminated.
According to the Centers for Disease Control and Prevention (CDC), the advantage of viral vector vaccines is that they provide protection against SARS-CoV-2 without having to risk infection with the real CDC virus and then producing antibodies.
The CDC also emphasizes that these types of vaccines do not actually infect the body with the CCP virus and that adenovirus cannot be used as a vaccine vector.
What is an mRNA vaccine?
Pfizer BioNTech and Moderna’s vaccine for the CCP virus uses mRNA technology, but this new technology had never been approved for widespread use until this CCP virus outbreak.
This technology uses messenger ribonucleic acid (mRNA), the molecule that provides genetic guidance to cells to make the proteins the body needs for a variety of cellular functions, including energy and immune defense.
In the laboratory, scientists have developed synthetic mRNA that directs human cells to produce the same unique stinger protein from the SARS-CoV-2 virus, which is also the target of a viral vector-based vaccine.
After the protein is made, the cells disrupt the genetic instructions and detach from them. Both Health Canada and the CDC emphasize that the mRNA never enters the center of the cell where the human DNA material resides, meaning that the vaccine does not affect or interact with the DNA in any way.
As with viral vector-based vaccines, the immune system recognizes the exogenous stinger proteins produced by the cells and produces antibodies against them to mount an immune response. If the immune system is confronted with a real SARS-CoV-2 virus, it can have antibodies to destroy the virus.
Although there are similarities between how vaccines for mRNA and vaccines for viral vectors direct cells to produce SARS-CoV-2 spike proteins, mRNA vaccines differ in that they do not contain any live virus.
Which vaccine is better now?
AstraZeneca and Johnson & Johnson have developed a viral vector-based vaccine for the CCA virus that is associated with a condition called vaccine-induced thrombotic thrombocytopenia (VITT), a coagulation syndrome that is extremely rare but potentially life-threatening if you get it.
The risk of developing this syndrome is estimated to range from 1 case in 100,000 doses to 1 case in 250,000 doses.
In Canada, where approximately 1.7 million doses of AZ vaccine have been used to date, only 7 cases of VITT have been reported.
Because the risk of VITT following vaccination with a vaccine using a viral vector is extremely low, the NACI recently reiterated that the mRNA vaccine is superior to other vaccines, which may be in the best interest of vaccinated Canadians.
Despite this recommendation, both Health Canada and NACI have emphasized that the vaccines produced by AZ and Johnson & Johnson are safe and effective for most people, as the consequences if infected with the CCP virus could be worse.
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