The Race for a Vaccine: Dr. Sanjay Gupta's coronavirus podcast for April 29

(CNN)A vaccine for Covid-19 could come faster than previous vaccines, but it could still be a year or more before one is widely available. CNN Chief Medical Correspondent Dr. Sanjay Gupta talks to a clinical trial participant and explains why this vaccine search is breaking barriers but will still take time.

You can listen on your favorite podcast app or read the transcript below.
Dr. Sanjay Gupta: If there's anything on the planet that everybody is hoping for, it's a vaccine for Covid-19. And all over the world, trials are underway.
    The timeline for the development has been compressed dramatically, with testing on animals and humans taking place at the same time. Usually animal testing comes at least a year before a vaccine would ever get to humans.
    But with the help of existing research on previous coronaviruses like MERS and SARS, the search for a Covid vaccine has become one of the fastest-moving in history. I'll explain the promise and the pitfalls during this race to get a vaccine.
    I'm Dr. Sanjay Gupta, CNN's chief medical correspondent. And this is "Coronavirus: Fact vs. Fiction."
    Sean Doyle: You can have nausea. You can sometimes develop fever, which may not be a bad response necessarily, 'cause that might indicate the immune system is mounting a response, meaning you could fight the virus in the future potentially, but you really never know what's going to happen.
    Gupta: That's 31-year-old Sean Doyle. He's one of a small handful of people in the United States testing a possible vaccine for Covid-19.
    When I spoke with Sean, he said his family and friends were nervous about his involvement with experimental medicine. But ultimately, they trusted his instincts as a medical student.
    And he's also had some practice. Sean was involved in a 2017 trial for an Ebola vaccine. He told me that the injection of the potential Covid vaccine into his arm was pretty mild.
    Doyle: It was not as bad as with other vaccines that I've gotten in the past. It really felt just like a flu shot. And after the tenderness subsided, after about a day or two, I really felt totally fine afterward.
    Gupta: Sean received his first dose of the vaccine in March at Emory University Hospital, where I'm also on the neurosurgery faculty.
    Doyle: So since then, I've returned at the one-week mark and the two-week mark post-vaccine administration and have given some blood samples so that the investigators can both assess my health, one, and two use those blood samples to see whether or not my body and other participants' bodies were able to mount an immune response, suggesting that should our bodies see the virus in the future it could be neutralized.
    Gupta: People like Sean are the only way vaccines can be proven effective for the population at large. While there are unknown risks for the early trial volunteers, it would be even riskier to skip these important testing stages.
    In 1976, when a new virus -- the so-called "swine flu" -- began sprea