How Do Vaccines Work?

By John Voudouris

Now more important than ever, vaccines have the ability to induce a strong immune response to a foreign virus. Throughout the many decades since this revelation, scientists have developed multiple ways to induce this immunity, including attenuated, inactivated, protein subunit, mRNA and viral vector DNA vaccines.

The first approach of vaccination is the attenuated vaccine which utilizes a weakened version of a virus that is harmless and is unable to replicate. Once injected into the human body, the immune system can copy the antigen and produce antibodies, successfully preventing cell necrosis from future interaction with that virus, as the antibodies would recognize the antigen and the killer cells would remove the virus. Specifically, the memory B cell remembers this antigen and prepares the immune system if this antigen is recognized again. The chickenpox and shingles vaccines are prime examples of this vaccine in use. The next example of a vaccine is the inactivated vaccine, which uses a similar approach of injecting a virus into the body. However, the viruses in this vaccine have been completely inactivated by heat or chemical methods after being grown in a lab. In summary, the difference between these two lies in being either alive (attenuated) vs essentially dead (inactivated).

The protein subunit vaccine utilizes the most important part of the virus to develop immunity: the spike protein. Instead of injecting the entire vaccine into an individual, the protein subunit vaccine injects solely the spike protein, which the immune system can use to produce antibodies. The pros of this vaccine are that they are easy and cheap to produce, as only the protein is necessary as opposed to the entire virus, meaning that inactivation is not necessary. Conversely, this vaccine can lead to a less strong immune response as the APC’s can have a more difficult time identifying the small protein if it is not attached to a virus. Hence, adjuvants (chemicals) are usually used in conjunction to increase this immune response.

In another approach, called the viral vector vaccine, scientists insert the genetic code for an antigen into a virus. The virus then delivers this code into the DNA of the host cells (in the human body), allowing them to create the antigen and stimulate antibody production once moved to the surface of these cells. This allows for this protein to be made very quickly as the viruses tend to spread very quickly. In addition, this approach can be very efficient as multiple genes can be added to the same virus to stimulate multiple antigen production at the same time.

Finally, the mRNA vaccine uses the mRNA of an antigen to start the spike protein production in each cell. Then, the cells place the spike protein on the cell membrane and the T cells copy this protein, while the B cells also place this protein on their membranes and produce antibodies. These are usually relatively cheap to manufacture and tend to create stronger immune responses as they create both antibodies and immune system killer cells (in most mRNA vaccines). The current mRNA vaccines, both

Pfizer and Moderna, use a similar approach to injecting mRNA into the body. They use nanoparticles to transport this mRNA, as opposed to simply injecting the raw mRNA which requires much more precise injections. Then, the genetic info is inserted into muscle cells to create antibody proteins. This is called the nucleic acid vaccine and has similar advantages and disadvantages to the mRNA vaccine, which is a type of nucleic acid vaccine.

Overall, vaccines can take multiple different paths to create antibodies that identify invading viruses. While some approaches may be more effective and efficient than others. All of these forms save lives. In the future, scientists will be able to better understand which vaccines are most effective for their target viruses and potentially develop new entire vaccines, minimizing potential side effects