What is the Difference Between mRNA and Adenovirus Vaccine?

The main difference between mRNA and adenovirus vaccines lies in their mechanisms of action and the way they deliver the genetic code for the target antigen, such as the SARS-CoV-2 spike protein. Here are the key differences:

1. Mechanism of action: mRNA vaccines deliver the messenger RNA (mRNA) molecules directly to the cells, which then produce the target antigen (e.g., the SARS-CoV-2 spike protein). This process bypasses the need for DNA transcription, allowing the immune system to respond quickly to the produced antigen. In contrast, adenovirus vector vaccines use an inactivated adenovirus to deliver the genetic code for the target antigen. Once the genetic material is inside the host cells, it is translated into the target protein.
2. Immunogenicity: mRNA vaccines seem to elicit robust initial neutralizing antibody (nAb) responses that decline over time, while adenovirus-vectored vaccines initially induce lower nAb responses but these responses catch up over time. The former includes vaccines like Pfizer/BioNTech and Moderna, while the latter includes AstraZeneca, Johnson & Johnson, and Sputnik vaccines.
3. Biodistribution: mRNA vaccines can display broad biodistribution, meaning they can reach and interact with various tissues in the body. In contrast, adenovirus vector vaccines primarily transduce local tissues following intramuscular immunization.
4. Production and complexity: Adenovirus-vector vaccines involve a more complex production process compared to mRNA vaccines. The complexity includes not only the production of the adenoviral vector but also the potential for pre-existing anti-vector immunity in the host, which can impair vaccine responses.

In summary, mRNA vaccines deliver the mRNA directly to cells to produce the target antigen, while adenovirus vector vaccines use an inactivated adenovirus to deliver the genetic code. mRNA vaccines show a rapid initial immune response that declines over time, while adenovirus vector vaccines have a slower initial response that increases over time. Additionally, mRNA vaccines have a broader biodistribution, and their production process is less complex compared to adenovirus vector vaccines.

Comparative Table: mRNA vs Adenovirus Vaccine

Here is a table comparing the differences between mRNA and adenovirus vaccines:

mRNA vaccines contain fully functional mRNAs that can be translated directly into the S protein, while adenovirus vector vaccines comprise additional layers of complexity, including production in cell cultures and purification steps. mRNA vaccines rely on multiple costly GMP steps, whereas adenovirus vector vaccines demonstrate the potential for easily generating large scale batches of adenoviral vectors. Both mRNA and adenovirus vector vaccines result in the production of native S proteins, which are intended to stimulate an immune response.