SPRINGFIELD, Ill. (AP) -- Early voting in Illinois for the March 17 primary is off to a slow start. But elections officials expect it to top the 520,000 early ballots cast in 2016.

Two phenomena could play a role.

Former Vice President Joe Biden's dramatic comeback this past week in the race for the Democratic presidential nomination has cleared a previously crowded field.

More voters might now take early ballots to choose between Biden and Vermont Sen. Bernie Sanders.

And the spread of COVID-19 caused by the novel coronavirus might prompt people to avoid polling place crowds and instead cast ballots early or by mail.