How herd immunity from coronavirus is developed

A safe and effective vaccine is not expected until at least 2021, so how does herd immunity work, and how can this method help in getting us back to our lives and preventing the spread of COVID-19?
3:22 | 05/20/20

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Transcript for How herd immunity from coronavirus is developed
You've heard that old saying their strength in numbers. Will it turns out numbers may be our greatest defense against the spread of code. It's called herd immunity. And the way it works is that once enough of us become immune to the virus spread of the virus floats and eventually the pandemic could dot. Thanks to vaccinations her community's been effective at eliminating polio smallpox until recently measles. Unfortunately we don't see lasting herd immunity against viruses mutate quickly. Flew where the common COLT. Herd immunity is a place we'd like to be with Covert and sooner rather than later. But how we get there it could happen naturally as the virus makes its way through our communities but that can be dangerous because as we've seen. Many people with Kobe beat him severely ill and for something you can actually be deadly. Then he's been wondering do people have some immune protection after they recover. Experts tell us they think that's true but it's not prove it and if it's true we're not sure just how long that immunity me last. But since herd immunity is our goal to know if we're there we first need to understand how fast the virus infects other people. That reproduction rate is what scientists call the are not fires. And for cold it that number is somewhere between two and three. That means each person with corona buyers can infect on average between two and three others. The second part of the herd immunity equation depends on us specifically how many of us are already immune. In a world where no one is immune to convene in each of us is at risk the virus can spread like wildfire. But imagine a world where there is hurting me say 75% of us are already in use. That means three quarters of the people exposed to anyone with a virus just won't get sick. So even if a few of us have the virus. The rest of us who are immune stop it from spreading. That's the kind of numbers game we're talking about. But it's not a game it's actually a formula based on that reproductive rate of the virus if knowing that we can figure out how many of us need to be immune for us to reach this week's for community. And that critical threshold for whom it is when one half to two thirds of the US population is immune. That leads somewhere between 150 and 216. Million Americans need to be immune. To meaningfully stop the virus from spreading throughout the country. The right now most experts say. We're probably a long way away from these kinds of numbers it. So just like with many other infectious diseases of the showstopper will be when most people can get a vaccine. Once we have one that's proven to work. And the great thing about it backseat is that it can help build a person's immunity but without making them sick. Until then we can all do our part to stop the spread of Coke through physical and social distancing washing our hands and sing home when sick. To learn more herd immunity visited abcnews.com.

This transcript has been automatically generated and may not be 100% accurate.

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