Covid-19 vaccines have put the end of the pandemic in sight, but success depends on getting shots into arms. Three CNN Heroes are working to bring these life-saving measures to populations who might otherwise be overlooked. Dr. Jim Withers delivers medical care to homeless people through Operation Safety Net, a program he started through his health system, Pittsburgh Mercy. Now, he is bringing the vaccine to them as well. "Driving to a site or making appointments online ... none of this is possible for folks who are living on the street," said Withers, a 2015 CNN Hero. "You really have to go to where someone is and cut down those barriers."