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  https://www.npr.org/sections/health-shots/2021/02/18/967462483/how-herd-immunity-works-and-what-stands-in-its-way?utm_medium=social&utm_term=nprnews&utm_campaign=npr&utm_source=facebook.com&fbclid=IwAR0Twq8K26CQpqac-qDjRLfDkzha-qQ6oyWGdN4M1T8O27SVKPwTsjxSlWI