That number isn’t high enough to fully reach herd immunity — and the flu still circulates every year. But there are benefits to partial immunity in the population: Only a fraction of adults are at risk of catching the flu in a normal year, and they can spread it less quickly, too. That means that the number of people at risk of dying is also much lower. Covid-19, unlike influenza, is a brand-new disease. Before this year, no one in the world had any immunity to it at all. And that means that, even if infection fatality rates were similar, it has the potential to kill many more people. One percent of a large number is bigger than 1 percent of a smaller number. “There aren’t 328 million Americans who are susceptible to the flu every fall at the beginning of the flu season,” said Andrew Noymer, an associate […]