While countries like the UK and the U.S. are moving quickly towards vaccine-backed herd immunity, too many other countries are nowhere near this goal. Former Prime Minister Gordon Brown joins the program to discuss global mass vaccination -- which he believes must receive highest priority -- as well as the life and death of Prince Philip.

Prince Philip passed away peacefully this morning just two months shy of his 100th birthday. In a statement, Buckingham Palace spoke of the Queen's "deep sorrow" at losing her beloved husband of more than 70 years. Simon Lewis joins Christiane to reflect on Philip's legacy in the monarchy. Lewis served as communications secretary to the Queen from 1998 through 2000.

In Vienna, momentum is building on the vital effort to revive the 2015 Iran nuclear deal. The United States and Iran are still not talking directly, and plenty of sticking points remain. For insight into the Iranians' position on the issues, Christiane spoke with Iran's Foreign Ministry Spokesman, Saeed Khatibzadeh.

Prince Philip was just 26 when he married then-Crown Princess Elizabeth -- in full pomp and pageantry -- in 1947. No one could have foreseen that the union would last some 73 years -- outlasting wars, scandals and countless global challenges to the monarchy. To reflect on the past 70 years, Christiane speaks with legendary historians Margaret MacMillan.

Like the Queen, Prince Philip was deeply committed to the commonwealth. Leaders of those nations have been paying tribute to the Duke including Australian Prime Minister Scott Morrison who said, "the commonwealth family joins together in sorrow and thanksgiving for the loss and life of Prince Philip." The Secretary-General of the Commonwealth of Nations reflects on the Duke's impact.

Dorothy A. Brown is a law professor and nationally recognized scholar in tax policy. She chose her field because she believed it was free from racism. She soon discovered how wrong she was. Her new book, "The Whiteness of Wealth: How the Tax System Impoverishes Black Americans and How We Can Fix It," draws on decades of research and personal histories, as she explains to Michel Martin.

The film "One Night in Miami…" is a fictional reimagining of an historic night. In 1964, Malcolm X, Sam Cooke and Jim Brown gathered in a Miami hotel room to celebrate the world heavyweight victory of Cassius Clay, soon to be known as Muhammad Ali. The film is the feature directorial debut of Oscar-winning actor Regina King. She joins the show alongside screenwriter Kemp Powers.

For many, the outcome of the trial of Derek Chauvin is a litmus test for racial justice and policing in America. Christiane discusses the stakes with former police chief Donald De Lucca and former federal prosecutor Laura Coates.

Phillip Atiba Goff is one of the country's leading scholars on law enforcement and race. Tracie Keesee is a former police captain with the Denver Police Department. They join Michel to explain how the Center for Policing Equity is working to strengthen the relationship between police and the communities they serve.

To reach the border, migrants must make long and arduous journeys from their home countries. VICE news correspondent Paola Ramos headed down to Colombia's border with Panama and joined migrants as they trekked through the dangerous jungles known as the Darién Gap. She spoke with Christiane about the experience.

Palestine is gearing up for its first election in fifteen years. Its outcome will have a major impact on U.S. policy and the elusive Israel-Palestine peace deal. Former Palestinian Foreign Minister Nasser al-Kidwa has formed a new independent party and is running in May's elections. He joins Christiane to discuss his platform.

Now, a musical odyssey to one of the most remote places on earth. Mahani Teave's love for classical music began as a child when the first piano arrived on Rapa Nui, or "Easter Island," as it was named by the first European explorer to arrive in 1772. But then she gave it all up to create the first music school at home. Mahani Teave joins Christiane from Rapa Nui to tell her fascinating story.

Health inequality was badly exposed during this pandemic, [but Priti Krishtel says it doesn't have to be this way. She is the Co-Founder and Executive Director of the non-profit Initiative for Medicines, Access & Knowledge. She spoke to Hari Sreenivasan about the need to rethink how patents are regulated.

Africa's terrorist group Boko Haram is responsible for hundreds of kidnappings -- even since the stunning 2014 abduction of nearly 300 Chibok schoolgirls. Everyone from Michelle Obama to Malala Yousafzai got involved in the hashtag campaign to "Bring Back Our Girls" -- a slogan that now is the title of a new book by Joe Parkinson, a definitive account of the incident and its aftermath.

President Joe Biden held his first formal press conference today. He addressed a host of urgent domestic issues including COVID, gun safety and immigration. On the foreign policy front, there is no greater challenge than China. The relationship between Washington and Beijing seems increasingly rancorous. Chinese ambassador Cui Tiankai joins Christiane to discuss the situation.

The battle to reform the Catholic Church has been plagued by a long-running sexual abuse crisis. Author, historian and journalist James Carroll argues that male dominance is the root cause of the church's issues. His new memoir, "The Truth at the Heart of the Lie," links his own crisis of faith as a priest to the history of the church itself. He joins Michel Martin to discuss his call for reform.

Tim O'Brien has been hailed as one of the best American writers of his generation. His groundbreaking book "The Things They Carried" drew on his experiences during the Vietnam War and was a finalist for the Pulitzer Prize. A new documentary, "The War and Peace of Tim O'Brien," focuses on his work and his life as a father. He joins Christiane from Texas.

This week, the head of the World Health Organization said it was "shocking" how little had been done to combat vaccine inequality and added that the gap is "becoming more grotesque every day." The WHO's Chief Scientist, Dr. Soumya Swaminathan, joins Christiane from Geneva.

Why is the universe the way it is? How did life begin? And how might it end? Astrophysicist Neil DeGrasse Tyson has spent his life in search of the answers. His new book, "Cosmic Queries," was co-authored with physicist James Trefil. Tyson joins our Walter Isaacson to discuss the book and what drives his thirst to explore the really big questions of the universe.

The U.S. is reeling from its latest mass shooting, which took place yesterday in Boulder, Colorado. This is the country's 7th documented mass shooting in the past week, coming barely 6 days after 8 people in Atlanta were shot to death, including six women of Asian descent. Journalist Dave Cullen, who has written the definitive accounts of the Columbine and Parkland shootings, joins the program.