mRNA Vaccines

Messenger RNA (mRNA) vaccines work differently than traditional vaccines. Most traditional vaccines use a weakened or inactive form of the virus that causes a disease to trigger an immune response. mRNA vaccines do not use the live virus at all. Instead, they teach our cells how to make a protein that triggers an immune response inside our bodies.

mRNA vaccines work by introducing a manufacturer version of mRNA that instructs cells how to make a protein that is unique to the virus. This protein is recognized by the immune system as foreign, stimulating the body's B-cells to produce antibodies. These antibodies will then recognize and fight the real virus if the person is exposed in the future. There are a few advantages to mRNA vaccines compared to traditional Vaccine Technologies. They can be developed faster because they do not rely on culturing a virus. The technology allows for easier production at large scale. mRNA also degrades quickly and does not integrate into human DNA.

A few potential drawbacks are that mRNA injections may cause more local and systemic side effects due to stimulation of the immune system. There is also limited data on very long-term safety and effectiveness for this platform. However, billions of doses of Covid-19 mRNA vaccines have now been administered without significant safety concerns. Ongoing research is helping to advance this promising new technology.

Viral Vector Vaccines

Viral vector vaccine technologies use a modified virus to deliver DNA instructions that teach cells how to make a protein from SARS-CoV-2. The goal is similar to mRNA vaccines in that it stimulates both arms of the immune system. However, instead of mRNA entering cells, DNA from the virus is delivered which can then make messenger RNA and subsequent proteins.

Typically, the vector virus is modified so it cannot replicate or cause disease. Common vectors include adenoviruses and poxviruses. Adenovirus vector vaccines for Covid-19, like Johnson & Johnson and AstraZeneca, deliver the SARS-CoV-2 spike protein gene. Once inside cells, the DNA synthesizes the spike protein and activates both antibody and T cell immune responses.

With viral vectors that can incorporate larger DNA segments, there is potential to develop multi-antigen vaccines against various pathogens or variants. Drawbacks include preexisting immunity against common viral vectors that may reduce effectiveness. Safety would also need ongoing evaluation since the vector virus is capable of gene delivery in host cells. However, current data suggests viral vector vaccines provide durable protection against severe disease with good tolerability.

Protein Subunit Vaccines

Conventional protein subunit vaccines present bacterial or viral proteins to stimulate antibodies without using a live pathogen. For Covid-19, purified spike protein or its receptor binding domain are often used. Recombinant DNA technology allows for mass production of these protein subunits in yeast, insect, or mammalian cell cultures.

After purification, the protein subunits are formulated with adjuvants, which are added to enhance the immune response. This may be necessary because proteins alone often do not efficiently stimulate both arms of adaptive immunity like T cells and B cells. Adjuvants like aluminum salts have been used safely for decades. Newer adjuvant systems try to mimic pathogen associated molecular patterns recognized by the immune system.

Protein subunit vaccines are generally very safe due to the lack of infectious agent. However, they may not confer as robust or long-lasting immunity as vaccines using live attenuated or inactivated whole viruses. New strategies are exploring cocktails of viral proteins or booster doses to broaden the immune response. Overall, protein subunit vaccines could offer a more stable product profile for global distribution compared to vaccines requiring cold chain infrastructure.

Traditional vaccines have saved millions of lives, new vaccine technologies
offer faster development and safer alternatives. mRNA, viral vectors, and protein subunits are leading platforms that provided the first authorized Covid-19 vaccines. The flexibility and scalability of these news approaches could accelerate responses to future pandemics. Continued progress in vaccine immunology and formulation may even enable multi-disease protection from a single dose. Overall, advanced vaccination strategies are increasingly empowering humanity to gain the upper hand against emerging infectious threats.

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