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mRNA Vaccines- It’s Worth a Shot

By Emily Liu

After months of living through a pandemic, there’s finally a faint light at the end of the tunnel – the newly developed COVID-19 vaccines. As I write this article, millions of doses are being produced and distributed around the world. There are several candidates that have shown good results in trials, but so far, the only vaccines that are officially authorized by the FDA are the ones produced by Pfizer-BioNTech and Moderna respectively. These two vaccines both proved to be about 95% effective at preventing healthy people from getting the disease, with mostly minimal side effects. They use a relatively new strategy of attack, one that could be the key to defeating the coronavirus as well as future viruses: mRNA. 

Most vaccines fall into one of four categories: live-attenuated, inactivated, subunit, or toxoid. Live-attenuated vaccines contain pathogens that are alive but weakened; inactivated vaccines contain dead pathogens; subunit vaccines contain only the parts of the pathogen that trigger an immune response; and toxoid vaccines contain “deactivated” versions of the toxins that cause symptoms. All of these help the body mount a defense against the “real” pathogen, but each type has its respective drawbacks. Live-attenuated vaccines may pose a danger to immunocompromised people who cannot fight off the weakened pathogen. Inactivated vaccines run the risk of not being able to induce an immune response, leaving the body unprepared. Subunit vaccines only work if the combination of pathogen parts is exactly correct; researching this combination takes time and money. Finally, toxoid vaccines only work on bacteria – not viruses. Thus, although these are all highly effective in the right situations, none of them are ideal when the whole world needs a vaccine against a virus ASAP. 

Enter the mRNA vaccine. It works on viruses. It does not use any whole viruses, inactivated or otherwise. It does not require tedious examination of each part of the virus. And it is neither expensive nor time-consuming to produce in mass quantities. In that case, how does it work? 

Viruses are essentially a bundle of genetic material in a protein shell. After a virus infects a host, it forces the host cells to make mRNA based on its own genetic material. mRNA (short for messenger RNA) is a type of genetic information that encodes instructions for making proteins, and viral mRNA contains instructions to make viral proteins. The host’s cells produce new copies of the virus and its proteins, and export them throughout the body, causing disease in the process. Where other types of vaccines would use whole viruses, mRNA vaccines only need the genetic material, not the virus itself. The full sequence of RNA in the novel coronavirus is already known; the corresponding mRNA can easily be produced in a lab. After receiving an mRNA vaccine, the host cells are able to produce viral proteins without producing complete viruses. This enables the host to synthesize “punching bag” versions of the disease-causing proteins (in this case, the spike-shaped protein on the coronavirus) without ever being exposed to the actual virus. The host’s immune system prepares a defense against these proteins, and it becomes more able to fight off the disease before it starts.  

The current mRNA vaccines both have a very high efficacy (i.e. success); however, this does not mean we can let our guards down now. There are many people who have yet to get their first dose, and both vaccines require two doses to ensure long-term protection. Beyond that, it takes a long time for the body to completely develop an immune response; it is dangerous to get a false sense of confidence immediately after vaccination. One article from CNN notes that an emergency room nurse tested positive for the coronavirus a full week after he’d gotten his first dose of the vaccine, and another nurse who received her second dose was still not immune for at least several days. As Eric Levenson writes, “The 95% efficacy number for the Covid-19 vaccines [assumes] some built-in wait time. Moderna measured the efficacy of its vaccine starting 14 days after the second dose, while Pfizer measured it starting seven days after the second dose.” 

On top of that, mRNA viruses mutate much more quickly than DNA viruses. The novel coronavirus has already mutated into multiple new variants, which the current vaccines may not be able to handle. A variant was discovered in the United Kingdom in the fall of 2020 – it was shown to spread more quickly than the original virus, and it is possible that they are linked to a higher death rate. Around the same time, a second variant was detected in South Africa, and a third variant was found in travelers from Brazil. These three new mutants were all detected in the U.S. by the end of January 2021. 

In light of the fast mutation rate, some scientists are looking to an additional approach: rather than designing a vaccine for each individual variant of the novel virus, they seek to develop a vaccine that will work against all coronaviruses, whether they already exist or have yet to emerge. Duke University’s Human Vaccine Institute aims to sequence the genomes of as many unique coronaviruses as they can, in order to find out which segments are essential to their function. Entos Pharmaceuticals is working to sequence the genomes, then synthesize a corresponding DNA sequence for injection. Moderna and Johnson & Johnson are looking to update their vaccines to account for new variants; immunologist Drew Weissman estimates that “a new RNA vaccine could be designed and manufactured for clinical testing within six weeks.” 

The vaccines and ongoing research are both huge steps forward, and they will make even greater of an impact if we remain vigilant. We need to continue following CDC guidelines, even if we have been vaccinated, even if everyone in the room has been vaccinated. This includes wearing masks, social distancing, washing your hands properly, and keeping surfaces clean. If we don’t tough it out for a few more months, we may end up having to tough it out for a few more years. 

That said, news of the mRNA vaccines is certainly something to celebrate. Not only is it a possible remedy for the pandemic, it opens the door to new possibilities for future vaccines. There is still much to learn about this strategy of attack against pathogens, but from what we’ve seen so far it’s worth a shot – or if you’re getting a COVID-19 vaccine, it’s worth two.