The next Covid-19 vaccine hurdle: Convincing millions of Americans they want the shot

In the coming months, America could reach a point when it has more Covid-19 vaccines than people want.

Between efforts from the federal government and drug companies to step up manufacturing and distribution, the US’s vaccine supply is truly increasing: At least 150 million doses are expected through March — a rate of more than 3 million shots a day, the kind of speed the country needs to reach herd immunity, when enough people are protected against the virus to stop its spread, this summer.

But public health experts are...