What about the mRNA vaccine?

There are several different vaccine approaches, mRNA vs. viral vector vs. subparticle vs. inactivated whole virus vs. attenuated virus.

All currently used vaccines use one of the latter 3 approaches.

Shingrix (new shingles vaccine) is particle based, meaning just a protein from the virus. So is the hepatitis B vaccine.

These two vaccines are amongst the most successful vaccines ever made.

Viral vectors are genetically engineered viruses, which can only infect one cell and then stop. They are used in the lab to express a given protein and have been used this way for decades. For a viral vector vaccine, the new viral gene is inserted into the vector, the viral vectors are then produced in large numbers and given to a person. Each viral vector can only infect a single cell once, produce the new viral protein and that is it. The person then will develop an immune response to the viral protein.

Inactivated viral vaccines are still used, although most have been replaced. The flu vaccine is inactivated influenza virus.

Attenuated viral vaccines have been very successful. Examples include measles, mumps, rubella, polio, and chickenpox vaccines. Typically, the attenuated viral vaccine works much better than the inactivated vaccine of the same virus.

mRNA vaccines take the genetic code of the new viral protein and make thousands and thousands of copies of the mRNA, which is then packaged into little particles. The particles, after injection into a person, are taken up by the cells and then the mRNA causes the cells to produce just that viral protein. Then, an immune response against that viral protein develops. So, this approach is not hugely different than just giving a person the purified viral protein. However, the mRNA approach theoretically induces a better cellular response. Purified protein vaccines induce primarily an antibody response. Theoretically, mRNA vaccines can induce both antibodies against the protein as well as a strong cellular response against the protein (or its peptides for those who know a little immunology).

As for Covid vaccines -

Pfizer and Moderna's vaccines are mRNA based.

Merck's, J&J'a and AstraZeneca's are single-cycle vector based.

Merck's is VSV, a favorite vector for virologists, because VSV vectors produce a lot of the new protein, whose gene is inserted.

The latter two use an adenovirus vector.

Novavax’s vaccine is simply a purified protein approach, meaning it’s just the spike protein in solution, like the hepatitis B and Shingrix vaccines.

Other companies are using inactivated SARS-CoV-2.

In short, there are several different approaches or technologies being tested in clinical trials.

So, it will be very interesting to see if one approach works much better than the other.

Tangentially, I am not sure why the SARS-CoV-2 spike protein or subparticle approach is not further along.

But we should know soon if intracellular expression of the spike protein is needed to protect against COVID.

Novavax's study uses just the purified spike protein, reportedly induces a strong humoral response (better than natural infection) and is now in phase 3.

If Novavax works well, then, presumably, there will be a quick switch to this vaccine since it is much easier to make and mass distribute a protein-based vaccine.

SMS