COVID-19 has led scientists to search for the right vaccine that will help us end this pandemic. The newest forms of vaccines are being developed meticulously, informed by centuries of vaccine research, and have shown great promise.
While all the scientific news may seem overwhelming, it’s important to note that vaccines have long aided our fight in eradicating diseases, among them smallpox and polio.
All vaccines introduce viral components or “antigens” to our immune system, and in response we produce antibodies. Binding of the antibodies to the antigens can both block a virus from infecting cells and activate the immune system to destroy the virus.
Even if these antibodies don’t stick around, the machinery that evolves to quickly produce the antibodies can — in the form of “memory B and T cells” — protecting us from future infections. This general mechanism of vaccines doesn’t change. However, the way we create vaccines has advanced tremendously over the last few centuries, bringing us to many new kinds of vaccines including synthetic RNA vaccines — leaders in the fight against COVID-19.
We have come a long way since the first vaccine was introduced. In 1796, Edward Jenner successfully created the smallpox vaccine — a vaccine consisting of cowpox, a similar virus. Jenner noticed that milkmaids who were exposed to cowpox did not get smallpox, suggesting that they were immune because of the cowpox. The first generation smallpox vaccine was made by isolating cowpox from inoculated animal skin, while the second generation vaccine was produced by growing cowpox in tissue cells. Tissue cells are better for making vaccines because they allow for large-scale vaccine production that animal skin models can’t provide, and they also offer reduced risk of contamination.
Since the creation of the first vaccine in 1796, scientists have discovered many more technologies that allowed for the global eradication of smallpox in 1977 and eradication of polio in the United States in 1979. The eradications were achieved through programs employed by the World Health Organization. Several types of traditional vaccines that emerged during the initial years after Jenner’s invention are still used today.
One common type is the live attenuated vaccine. For this vaccine scientists reduce the virus’s harmful effects and that modified virus is then used as the vaccine. Live attenuated vaccines are used to protect against measles, mumps, rubella, varicella and rotavirus. Many manufacturers create attenuated vaccines by infecting non-human cell cultures with the virus. This infection process is repeated hundreds of times, causing the virus to mutate and adapt to the new environment. In so doing, the virus becomes essentially harmless to humans. Live attenuated vaccines are commonly used because of their cost-effectiveness and because they are purported to produce a more natural immune response, but they can cause serious health complications in immunocompromised people. Another challenge of live attenuated viruses is that they can mutate back into a virulent form that can cause disease in humans.
Another type of traditional vaccine — inactivated vaccines — don’t carry this risk. For inactivated vaccines, the virus is killed but kept intact so that the human immune system can still recognize it. Unfortunately, inactivated vaccines only provide short-term immunity. The number of antibodies your body produces to fight off the virus begins to decrease over time and fewer memory B and T cells are generated than for live attenuated viruses, which is why we sometimes need periodic booster shots. Some examples of diseases treated using inactivated vaccines are polio and rabies.
All these previously mentioned vaccines use entire organisms, but there are also vaccines that are made from only one part of a pathogen. For example, the hepatitis B vaccine consists of a single protein — the hepatitis B surface antigen. It can be much more convenient and safer to work with a single component of an organism rather than with an entire organism, and a single component can be just as effective. Using only a part of the virus allows the body to implement a robust and specific immune response comparable to using the entire virus.
Today, scientists are looking at even newer technologies in hopes of engineering vaccines that are even more convenient to prepare and provide more effective immunity with fewer side effects. The leading COVID-19 vaccines from Pfizer and Moderna are the first FDA-approved mRNA vaccines. mRNA is the genetic material that serves as a blueprint for the production of proteins in our body. The RNA vaccine gives your cell the instructions to make a viral protein, which triggers your immune system to make antibodies for that protein and respond to the disease upon infection. Not only can your immune system learn how to recognize and destroy a given virus without facing infection, but it can do so very efficiently.
The Pfizer and Moderna COVID-19 vaccines are estimated to be 95% effective at preventing the disease. In addition, the production of RNA vaccines is very efficient compared to that of traditional vaccines. RNA vaccines can be produced more easily than the corresponding protein-based vaccines and unlike live attenuated and inactivated vaccines, their production doesn’t require the use of live, potentially dangerous cells.
DNA vaccines, another new type of vaccines, work very similarly to RNA vaccines. DNA is the basis of our genome; it codes for everything our body needs to function. Our body often translates DNA to RNA to provide blueprints for proteins. Like RNA vaccines, DNA vaccines provide genetic information that codes for a viral protein. However, DNA vaccines have a few more risks than RNA vaccines, including the possibility of altering your cell’s natural genome. Viral vector vaccines, another recent type of vaccine, are similar to DNA and RNA vaccines, but the virus’s genetic information is housed in an attenuated virus (unrelated to the disease-causing virus) that helps to promote host cell fusion and entry.
Scientists are interested in all these types of new vaccines for addressing COVID-19. As mentioned above, the leading vaccines from Pfizer and Moderna are RNA-based, and AstraZeneca’s front-runner is a viral vector vaccine. Experimenting with different vaccines allows companies to determine which one is the most effective. It also gives several options to the public when vaccines are distributed. Regardless, all these vaccines safely provide your cells with the ability to tag and destroy COVID-19 viruses, teaching your immune system how to respond effectively.
Scientists are continually making breakthroughs in vaccine science to better protect us from deadly viruses. Even with the advent of a COVID-19 vaccine, the research doesn’t end, as scientists will apply these newer technologies to develop vaccines for other life-threatening illnesses.