Previously, we discussed how fear of the unknown leads to reduced trust in science, while also explaining how effective scientific communication helps build trust by raising the public’s collective understanding. Knowing that overcoming vaccine skepticism will be crucial for preventing SARS-CoV-2 transmission, we put science communication ideas into practice with a brief introduction to mRNA vaccines.

Researchers are continually expanding the immunization toolbox. Vaccines have already saved millions of lives and eradicated some diseases entirely, but modern medicine seeks to apply vaccine technologies to an ever-widening array of diseases. Conventional vaccines have proven difficult to develop for certain diseases, including rapidly-evolving pathogens like HIV and influenza. mRNA vaccines offer a new approach that could allow scientists to respond more quickly and effectively to emerging disease threats like COVID-19. mRNA vaccines also have potential immunotherapy applications against cancer and other non-infectious diseases.

How mRNA Vaccines Work

Traditional vaccines generally involve introducing inactivated pathogens or pathogen-specific molecules—such as their proteins or carbohydrates—into patients in order to act as antigens that stimulate the body’s natural adaptive immune response. This initial response leaves the immune cells primed to attack any actual disease-causing cells or viruses that should appear in the future.

Instead of directly introducing viruses or antigens, mRNA vaccines prompt the body’s own cells to produce disease-specific antigen proteins. Once introduced into a cell, engineered mRNA transcripts are translated into protein by the cell’s native ribosome, just like any other RNA transcript. When the synthetically-encoded antigen protein is expressed on the cell’s surface, the immune system recognizes it as foreign and learns to attack those antigens, priming the system against future exposure to that disease.

Like conventional vaccines, mRNA vaccines will likely be delivered to patients via injection or nasal spray. Injections can target the skin, bloodstream, muscle, lymph nodes, or even specific organs or tumors.

Pros and Cons of mRNA Vaccines

Lower costs and ease of production may be the greatest advantages of mRNA vaccines, especially when facing emerging diseases such as Zika, Ebola, or COVID-19. While conventional vaccines often require complex reagents and mammalian cells, custom mRNA strands are quite simple to produce in laboratories using readily available materials. Although mRNA vaccines have not yet entered commercial production, proponents of the technology claim that it will be easy to scale up rapidly to meet the needs of mass immunization programs.

mRNA vaccines may also be safer than traditional vaccines. mRNA transcripts degrade and disappear within a matter of hours, leaving behind the encoded proteins that perform their functions until they, too, are degraded in a matter of days. This transience minimizes the risk of multisystem inflammatory syndromes and other side effects that can come from introducing other foreign agents.

However, this transience may also present the greatest barrier for mRNA vaccines. Naked RNA molecules are notoriously unstable in vivo, with RNases waiting to degrade extracellular RNA. Vaccine engineers must design delivery methods that not only protect the mRNA from this degradation but also facilitate its uptake into cells.

Next Steps and Applications for mRNA Vaccines

As of November 2020, no mRNA vaccines have been approved for clinical distribution. However,  Moderna and Pfizer are currently in Phase 3 clinical trials of mRNA-based vaccines against SARS-CoV-2. These clinical trials will further validate these vaccines’ safety while examining whether they can provoke sufficient immune response to prevent COVID-19 infection. Researchers also seek to determine how long mRNA vaccine-induced immunity might last—a question that has loomed large in the field. Data from these trials could inform and accelerate the development of other mRNA vaccines.

mRNA vaccines could extend beyond infectious diseases to form the basis of immunotherapy treatments for other diseases, including cancer and even allergies. Many mRNA vaccines currently under development target blood cancers or tumor cells. This technology is particularly ideal for oncological applications because researchers can develop personalized vaccines for cancers that differ genetically from patient to patient.

For a deeper dive into the details of mRNA vaccines and their development, check out this Nature review.

Separately, if you are having trouble parsing out the flurry of new information and data surrounding COVID-19 and vaccine development, take a look at our guide to critically evaluating scientific information and our blog on how the pandemic has changed scientific communication.