The rise of the Delta variant has prompted a thorny question: Do we need a booster dose of the vaccine for Covid-19? Vaccine makers think so, but regulators are yet to be convinced.Principles are also at stake: Should richer countries be talking about administering extra doses when so many people around the world are yet to receive even a single shot?Guest: Rebecca Robbins, a business reporter covering Covid-19 vaccines for The New York Times. Sign up here to get The Daily in your inbox each morning. And for an exclusive look at how the biggest stories on our show come together, subscribe to our newsletter. Background reading: Although studies of a third dose are underway, experts agree that the vaccines are still working well. Here’s what to know about the potential booster dose.U.S. officials said that the decision to go ahead with a booster shot would depend partly on how many infections cause serious disease or hospitalization in vaccinated people.For more information on today’s episode, visit nytimes.com/thedaily. Transcripts of each episode will be made available by the next workday.