Artistic director of Guild Hall, where the production is set to take place, Josh Gladstone, told the New York Post's Page Six: "We have a requirement now along the lines of what Actors' Equity is requiring, and what Broadway is requiring, for performances.
"So yes — we're very excited with the cast that we have, and we're delighted Susan has put together a beautiful evening.
"We're sorry not to have Laura on this, [and] we will look forward to working with Laura again. We are concerned about maintaining the safety of our staff and our audiences."
However, a representative for Guild Hall added: "The policy of Guild Hall is that performers have the option to provide proof of full vaccination or a recent negative Covid test result."
The rep confirmed that Osnes has left the show but did not give any details on why.