A nurse walks towards the Roger Salengro Hospital in Lille, France, where two patients were diagnosed with a coronavirus related to SARS. Michel Spingler/AP hide caption

itoggle caption Michel Spingler/AP

A baby receives a polio vaccine at the Medina Maternal Child Health center in Mogadishu, Somalia. The country has one of the lowest immunization rates in the world. Ben Curtis/AP hide caption

itoggle caption Ben Curtis/AP

A man smokes a cigarette as he takes a break at a fruit market in Hyderabad, India. Smoking tobacco is eight times more prevalent among Indian men than women. Noah Seelam/AFP/Getty Images hide caption

itoggle caption Noah Seelam/AFP/Getty Images

More than a hundred different species of Anopheles mosquitoes can transmit malaria to people. Adam Cole/NPR hide caption

itoggle caption Adam Cole/NPR

There's no better deal than getting polio cases down to zero, philanthropist Bill Gates says. Marie McGrory/NPR hide caption

itoggle caption Marie McGrory/NPR

Scientists in the U.S. are growing the H7N9 virus in the laboratory to help with vaccine development. James Gathany/CDC/Douglas E. Jordan hide caption

itoggle caption James Gathany/CDC/Douglas E. Jordan

Influenza covers it's shell with two types of accessories: the H spike, blue, and the N spike, red. Here the flu particle is sliced open to show its genetic material. Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases hide caption

itoggle caption Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases

A health worker weighs a Somali baby on scales at a medical clinic in Mogadishu. Babies in Somalia have the highest risk of dying within the first 24 hours after birth. Carl de Souza/AFP/Getty Images hide caption

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Abdullah Mchumvu has been training African giant pouched rats for more than a decade in Morogoro, Tanzania. Jonathan Kalan for NPR hide caption

itoggle caption Jonathan Kalan for NPR

A baby receives a polio vaccine at the Medina Maternal Child Health center in Mogadishu, Somalia, on Wednesday. Somalia has one of the lowest immunization rates in the world. Ben Curtis/AP hide caption

itoggle caption Ben Curtis/AP

A health worker collects pigeons from a trap at People's Square in Shanghai, China, earlier this month. So far, workers have tested more than 48,000 animals for the H7N9 flu virus. ChinaFotoPress/Getty Images hide caption

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