The first SARS-CoV-2 vaccinations have been approved by the FDA, marking a possible turning point in the COVID-19 pandemic. These vaccines, which use messenger RNA (mRNA) to trigger the body’s immune system to produce antibodies against the virus, are faster to produce than traditional vaccines. A report published in August details the early phase trial that supported the development of the vaccine.

Traditional antiviral vaccines are created by growing attenuated, or weakened, copies of a virus inside living cells from chicken eggs or mammalian cell lines. The attenuated virus or a portion of it is then injected into humans to promote immunity. The new mRNA-based vaccines contain the genetic material to encode a single viral protein that, when injected into the body, induces antibody production against the target protein. In this case, the target viral protein is a spike glycoprotein that facilitates movement of viruses across the cell membrane. Because mRNA degrades easily, it must be encapsulated in lipid nanoparticles in order to be absorbed by cells.

The investigators gave participants two vaccines, 28 days apart, in doses of either 25, 100, or 250 micrograms per vaccine. They collected participants’ blood at multiple time points after vaccination to measure antibody titer (concentration), neutralizing ability, and immune response.

After the second injection, all three doses produced antibody titers similar to those found in the serum of people who had recovered from SARS-CoV-2 infection. The antibodies were also equally effective in neutralizing the virus as those in convalescent serum. Both the 25- and 100-microgram dose groups exhibited an increase in helper T cells, but only the 100 microgram group showed an increase in cytotoxic cells, which are important for destroying virus-infected host cells. The participants reported no serious adverse events and only one participant dropped out of the trial due to effects of the vaccine.

Following this report, development of the mRNA vaccine continued and gained approval by the FDA in December 2020. The authors noted that development of a traditional vaccine may have taken years, while theirs took only two months.

• Link to full report.