Animal caretakers understand the concept of vaccines, whether they’re ones used to keep groups of livestock healthy, their dog safe from rabies, or even ones they receive themselves before flu season. Another vaccine we’re learning more about is the one against COVID-19. How are COVID-19 vaccines different from the ones livestock producers are used to?
It turns out COVID-19 vaccines are quite different from those we use in animals. The technology used to create them is substantially advanced compared to the vaccines we’ve used over the years.
To review what we learned in science class, vaccines trick the body into thinking it’s been exposed to an infectious germ. The immune response generated by the vaccine is “remembered” by the body when it actually becomes infected with the germ. The result is that disease effects are prevented or greatly diminished in the vaccinated animal.
To accomplish this, typical vaccines contain the same germ (or parts of it) we want the body to respond to immunologically. Animal vaccine manufacturers either treat the germ to kill it (while preserving enough of the structure for the immune system to respond to) or artificially grow it such that it can still multiply in the body, yet not cause illness. Killed vaccines such as our dog’s rabies vaccine are examples of the former, while modified-live vaccines (e.g., intranasal pneumonia shots given to calves) exemplify the latter.
Which of those types describes the COVID-19 vaccines? Neither one, exactly. The initial COVID-19 vaccines approved (Pfizer and Moderna products) use technology that makes killed or modified-live vaccine technology seem ancient.
Unlike most animal vaccines, these COVID-19 vaccines don’t contain the germ itself. They use an artificially created protein molecule called messenger RNA (mRNA). Messenger RNA is used by cells all the time to instruct their internal machinery to make the essential proteins needed for cell survival and function.
The COVID-19 coronavirus uses its “spike protein” to infect cells in our bodies. Think of the spike protein as a “hook” that allows it to attach to and invade a body cell (a cell lining our lung surface, for example). The COVID-19 mRNA vaccine works when the mRNA molecule gets into the regular cells in our body and tells them to make a duplication of that spike protein. Our regular cells then stick that duplication out on their surface for the immune cells of the body to respond to. And respond they do, making antibodies that bind up the spike protein on any actual COVID-19 virus or destroying any body cells that have already been infected, cutting off the virus’ reproduction.
Therefore, instead of relying on the vaccine germ itself to alert the body’s immune system, mRNA vaccines essentially tell the body to naturally “make” the part of the germ to which the body will respond. Because mRNA is just a simple chain of molecules, there’s no way it can cause the disease.
One peculiarity of mRNA molecules in general is that they have very short lifespans – usually measured in hours. Therefore, mRNA vaccines need to be stored and shipped in very cold temperatures in order to preserve the molecule. In addition, the mRNA molecules are coated such that they aren’t degraded by the body before they can get into our cells.
Another COVID-19 vaccine (the AstraZeneca product) uses different, yet still very advanced, technology. This vaccine consists of a live, harmless virus into which a specific gene is inserted. This gene tells the harmless virus (an adenovirus) to show the COVID-19 spike protein on its surface and stimulate the immune system that way.
Even though these vaccines use unusual technology, their trial results very good compared to most other vaccines. This creates the promise that these technologies might be useful to create vaccines against other diseases – of animals as well as people – in the future.