The World Health Organization says there are 25 potential coronavirus vaccines in clinical trials internationally.

Here in the United States, the government has put its money behind several different vaccine candidates through Operation Warp Speed.

One of those vaccines is being developed by the Vaccine Research Center at the National Institutes of Health's National Institute of Allergy and Infectious Diseases, in partnership with the biotechnology company Moderna. The vaccine is expected to enter Phase 3 testing next week. This phase of the trial is expected to involve 30,000 volunteers and will test whether the vaccine protects people against the coronavirus.The vaccine uses messenger RNA (mRNA), which are cells used to build proteins -- in this case, the proteins that are needed to build the coronavirus' spike protein, which the virus uses to attach itself to and infect human cells. Once the immune system learns to recognize this target -- thanks to the vaccine -- it can mount a response faster than if it encountered the virus for the first time due to an infection.

Early results from the Phase 1 study were published in the New England Journal of Medicine in mid-July. The study showed that the vaccine, given at three different doses, triggered an immune response in the people who received it (the higher the dose, the higher the immune response). More than half of the participants experienced side effects including fatigue, chills, headache, muscle pain and pain at the injection site. The Phase 3 trial will involve the middle dose --100 micrograms (µg).

Dr. Barney Graham is the deputy director of the Vaccine Research Center. He spoke to Dr. Sanjay Gupta to explain a little bit about the technology behind the Moderna vaccine. What follows is a portion of their conversation, edited for length and clarity, to explain what is happening inside the body.

Dr. Sanjay Gupta: How does the vaccine work -- you're giving a little portion of messenger RNA [mRNA] to somebody. What is the mRNA and how does the body respond and create these antibodies?

Dr. Barney Graham: Our human genome is made of DNA; this is a double-stranded molecule. Most people have heard of DNA. The way our body makes proteins is that, from the DNA template that is made of nucleotides [basic building blocks], it does something called transcription: It uses its DNA template to make an RNA template. So, the RNA is the template we use in our own body normally to make proteins that are necessary for cell function ... and that part is called translation ...

And so when you put RNA directly into the muscle cell, by injecting it in as a vaccine, that RNA goes right into the cytoplasm [the body, not the nucleus] of the cell, is translated by the ribosomes to make a protein. And in our case, the mRNA that we use to make this protein is our vaccine. And when that RNA goes into the muscle cell, it creates and produces a protein, and when that protein is sitting on the muscle cell, it looks just like the protein that wou

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