COVID-19 Vaccines, Explained

Over the weekend, the United States Food and Drug Administration (FDA) issued an Emergency Use Authorization (EUA) for a third COVID-19 vaccine from Janssen Biotech Inc. (a Pharmaceutical Company of Johnson & Johnson). Two other COVID-19 vaccines, from Pfizer-BioNTech and Moderna, currently have EUA for use in the U.S., with several others in late-stage trials or approved internationally. So how do these new vaccines work? And will they bring an end to the masks, social distancing, and regular testing that’s become part of our lives?


mRNA Vaccines

Pfizer-BioNTech and Moderna’s approved vaccines are messenger RNA (mRNA)-based. They carry only the genetic instructions to make the spike protein that decorates the outside of SARS-CoV-2 (the virus that causes COVID-19) rather than the protein itself. After vaccination, our bodies’ cells take up those mRNA instructions and use them to make the virus spike protein. Immune cells recognize this protein as foreign and generate antibodies against it to protect us if the actual virus subsequently infects us. These mRNA vaccines are designed to have a second booster shot a few weeks after the first to generate a high enough amount of antibody production.

Importantly, since just the mRNA instructions to make a single viral protein are used, this cannot become incorporated into our own DNA genome and cannot produce infectious viruses that could infect anyone else or cause us to test positive in a COVID-19 PCR test. The mRNA also degrades in our body over time, so we don’t continue to make viral proteins. Encoding viral proteins using mRNA is a relatively new vaccine technology, but it has been in development for decades as scientists optimized ways of stabilizing fragile mRNA molecules.


Viral Vector Vaccines

Other types of COVID-19 vaccines currently in trials or approved in other countries use more traditional approaches. The Oxford–AstraZeneca vaccine approved in Europe and the Sputnik V vaccine approved in Russia each delivers the gene to make the coronavirus spike protein in a harmless adenovirus vector. This vector can enter cells, causing them to make spike protein, but can’t replicate. A key advantage of this type of vaccine is it is more stable. It can be stored for months in a refrigerator, simplifying distribution to regions far from major hospitals or in countries with limited health infrastructure. In contrast, the mRNA vaccines must be either shipped at ultracold temperatures (Pfizer) or refrigerated only for a few weeks (Moderna) to keep them intact.

The Johnson & Johnson vaccine, which recently reported positive trial data, similarly uses an adenovirus vector but requires only a single shot providing a further logistical advantage. As of Monday, March 1st, millions of doses of the new vaccine were already starting to be distributed.


Other Vaccines

Other vaccines in the late stages of trials include those by Novavax and Sanofi, which contain pre-made virus spike protein. This is an established approach to vaccine design (for example, the hepatitis B vaccine in use since the 1980s is also protein-based), so existing manufacturing facilities and expertise should allow rapid large-scale production.


The Outlook

Initial data for the Moderna and Pfizer RNA vaccines showed they both prevent disease in about 95% of people vaccinated. However, since the earliest trials began in summer 2020, we don’t know how long this protection will last. A COVID-19 vaccine could become an annual shot we get used to taking or something we just need a booster for every few years. We also don’t know how the vaccines will impact whether someone can still pass on the virus. However, given that they lead to less severe illness, we can be hopeful that they may also reduce transmissibility.

One thing we can be sure of is that, until most people are vaccinated, it will be important to continue with mask-wearing and social distancing measures. Testing for COVID-19 also remains a top priority to ensure we are not passing the virus on to vulnerable people in our communities.

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