It’s the idea that drives campaigns to vaccinate every American against illnesses like the flu or measles. However, even without a vaccine, the term “herd immunity” has surfaced as a strategy to combat COVID-19. On Monday, national media personalities including Ann Coulter and Rush Limbaugh brought it to the forefront. “I think it will be the solution,” said Zachary Martin, who lives in Pittsburgh. “We could use mitigation to achieve herd immunity with low risk.”The idea is that when enough people become infected with the virus or vaccinated against that the spreading stops.“I think herd immunity is only possible if we develop a vaccine,” said Julia Yudkobizz, who lives in Squirrel Hill.On Monday, Pittsburgh’s Action News 4 spoke with Dr. Mark Roberts, the chair of the Department of Health Policy and Management at the University of Pittsburgh, about herd immunity.“The problem is that in the absence of a vaccine, the only way to develop herd immunity is to get people to be infected and recovered,” said Dr. Roberts.He said a vaccine is necessary for herd immunity to work. “The problem is we are way, way below the level that’s required of herd immunity for COVID-19,” said Dr. Roberts.About 1.2 million people live in Allegheny County. According to Roberts, for herd immunity 60% or about 700,000 people need to contract and recover from the virus. However, he said 1% of COVID-19 cases are fatal.“That’s a huge number of deaths in Allegheny County to achieve herd immunity,” said Dr. Roberts.Dr. Roberts said if we continue without vaccine, eventually we will achieve herd immunity but it comes at a cost of lives lost and overwhelmed hospitals.