Just one year after the World Health Organization declared the novel coronavirus a global pandemic, three COVID-19 vaccines are available in the United States, and more than 2 million Americans are receiving shots each day. Americans are eager to get back to business as usual, but experts caution that opening the economy prematurely could allow a potential resurgence of the virus. How foot traffic patterns in restaurants and bars, schools and universities, nail salons and barbershops affect the risk of transmission has been largely unknown.