Bill and Melinda Gates addressed their traditional annual public letter this year to Warren Buffett, the legendary investor and longtime friend of the couple who in 2006 committed to donating most of his wealth to the Gates Foundation. The Berkshire Hathaway chairman’s gift was valued at more than $30 billion at the time, and brought together the fortunes of the world’s two richest men in a common philanthropic effort. In their account for Buffet of the foundation’s work, the Gates make the case for optimism, rooted in progress over the past few decades fighting extreme poverty and childhood mortality. They say 122 million children’s lives have been saved since 1990 thanks to a reduction in mortality rates. “There is no greater value than this,” Bill Gates writes in the letter. “Saving children’s lives is the best deal in philanthropy.” The Gates cite vaccinations and contraception as two of the most effective investments in saving and improving lives. “For every dollar spent on childhood immunizations, you get $44 in economic benefits,” they write. “That includes saving the money that families lose when a child is sick and a parent can’t work.” It now costs less than $1 for a vaccine that protects against five deadly infections. Their letter includes an extended discussion of contraception’s role in reducing poverty and infant mortality. “Like vaccines, contraceptives are one of the greatest lifesaving innovations in history,” the Gates write. ”Contraceptives are also one of the greatest antipoverty innovations in history.” The Gates argue that giving women control over when they have babies results in healthier, better-educated children, and mothers who can more fully participate in the workforce. “I believe in universal voluntary access to contraception. Full stop,” Melinda Gates said in an interview. ”I’ve seen it transform millions of women’s lives around the world.” Over 300 million women in developing countries now have access to modern contraception, while an estimated 225 million more want it but don’t have adequate access. The Gates Foundation is part of a group aiming to extend contraception to 120 million more women by 2020. New ways of delivering contraception include a simple shot that prevents pregnancy for three months. The Gates cite newborn deaths and childhood malnutrition as ongoing challenges. While overall childhood deaths are down, newborn deaths now represent 45% of all childhood deaths, compared with 40% in 1990. Last year, 2.5 million children died during their first month of life. And nearly 45% of childhood deaths are linked to lack of sufficient nutrition. Richer countries do better than poorer ones, but “nutrition is still one of the biggest mysteries in global health,” Bill Gates writes. The Gates said their disappointments include the lack of an HIV vaccine, creams to block HIV infection, a stronger malaria vaccine, and a tuberculosis vaccine. But they also make some bold predictions about the near future: “Polio will soon be history. In our lifetimes, malaria will end. No one will die from AIDS. Few people will get TB. Children everywhere will be well nourished. And the death of a child in the developing world will be just as rare as the death of a child in the rich world.” In passing, the Gates briefly touch on the current global political turbulence, acknowledging “dramatic political transitions… including new leadership in the United States and the United Kingdom.” In an interview, Bill Gates said he hoped that the US and UK continue to fund important global public-health efforts. Melinda Gates said populism and isolationism were among her biggest concerns right now: “If people turn too inwards to look at their country and don’t continue to look at the world at large, we won’t have peace and security in the world.” “By preventing the spread of disease, we save lives in other countries and at home,” the Gates write in their letter. “By stimulating economic development, we open new markets for our countries’ goods. By making conflict less likely, we advance our own national security. And by lifting up the poorest, we express the highest values of our nations.”