There are many strategies when it comes to developing a vaccine, but the idea behind all of them is similar. Vaccines are designed to pose a foreign invader, such as a virus or bacterium, to your adaptive immune system without causing you to be sick. Our immune systems are quite amazing, which also makes them quite complex. Here, we will focus on a few aspects that are important for understanding vaccine development.
Two major types of cells recognize diseases in our immune system, flush them out, and build ‘memory’ for our immunity against later invasions: B cells and T cells. These adaptive immune cell types can work independently or together to fight infection and build memory against re-exposure towards the invader (e.g., the virus, bacterium, parasite, cancer cell, etc.). T cells have the ability to kill these invaders directly, recruit other immune system cells to the site of infection, and aid in the development of B cells. They are also able to confer memory through the release of proteins called cytokines. B cells release Y-shaped proteins called antibodies, which similarly recognize invaders and work to destroy them. When something foreign enters our bodies, B cells begin to create antibodies against that invader. While these cells are amazing at protecting our bodies from infection, this process takes time (about 7 days for the adaptive immune system). However, once our immune system is ‘primed’ with a particular invader, it can produce antibodies against this invader very quickly when exposed to it again, preventing re-infection. The use of vaccines gives our immune system (including our B and T cells) a template to develop immune memory against re-infection without experiencing the full onset of symptoms viral exposure generates.
So, how do vaccines coax our immune system into providing a defense against viral infections? There are many different vaccine types, but they all use parts of the virus to trick our immune system into creating antibodies against that virus, effectively ‘priming’ our immune system to be ready to quickly generate antibodies when we are exposed to the real virus. As you can imagine, there are many different parts of a virus to choose from when creating vaccines, and some viruses are more difficult to develop a vaccine against than others. Viruses such as the flu can mutate rapidly, which is why we need a new flu shot each year to protect us from the most prevalent flu strain. In fact, many RNA viruses can mutate quickly, creating new strains that may need a different vaccine to be effective. Coronaviruses, such as COVID-19, are RNA viruses (read more about the novel coronavirus here).
There are many different types of vaccines that are currently in development for COVID-19, three of which have been approved for emergency use in the U.S. This post focuses on the two vaccines made by Moderna and Pfizer, which are called mRNA vaccines. For the hesitant people who realize that these are a new type of vaccine, it is important to note that this type of vaccine is backed by more than 10 years of research. mRNA, or messenger RNA, is composed of genetic code for synthesizing proteins. The cellular machines in our bodies read mRNA and use it to build the proteins that are in our cells. Viral proteins are also made by the same machines our cells use. So, a mRNA vaccine for the novel coronavirus contains mRNA that encodes for one of the virus’ proteins. Once someone is administered the vaccine, the mRNA in the vaccine is taken up, synthesized by our cells, and presented to the adaptive immune system to ‘prime’ it, just as the adaptive immune system would be primed after a natural infection. B-cells then have the ability to recognize the foreign invaders and create antibodies against it so that the protein could be cleared. Given that our B-cells have a memory of when and if we are exposed to COVID-19, our body can recognize it and mount an immune response faster, causing it to clear our system before it has time to infect us. It is important to keep in mind that this protein is not an infectious virus, but rather one piece of the virus as a whole. Therefore, mRNA vaccines cannot cause an infection. If you would like to learn more about mRNA vaccines, read this blog post here.
With three vaccines now available for emergency use, we should see a light at the end of the pandemic tunnel very soon. To find out who is currently eligible for vaccination in the state of Indiana, check here! As always, stay safe and stay informed!
I would like to thank my brother, Walter Harrington, Ph.D., for providing information on vaccine development and sources pertaining to Moderna’s vaccine trial. I would also like to thank my friend Monica Moran for helping me break down the adaptive immune response to a level of understanding for everyone.
Krishnamoorthy, Prabu. “How do Clinical Trials Work? – Infographic.” GraphicsPedia, https://graphicspedia.net/how-do-clinical-trials-work-infographic/.