Those agencies are already falling short, as we saw last year, when they couldn’t effectively respond to the Zika threat. What will they do when we face a real pandemic? With 7.4 billion people, 20 billion chickens and 400 million pigs now sharing the earth, we have created the ideal scenario for creating and spreading dangerous microbes. Trade and travel have connected most points on the globe in a matter of hours. More and more people are living in the microbe-rich megacity slums of the developing world.

By some estimates, the 1918-19 “Spanish” influenza killed more people than all the wars of the 20th century combined. Today, an influenza pandemic could be more devastating than an atom bomb. We are already witnessing an outbreak of influenza in birds — the H7N9 strain, in China — that could be the source for the next human pandemic. Since October, over 500 people have been infected; more than 34 percent have died. Most victims had contact with infected poultry, yet three recent clusters appear to be from person-to-person transmission. Will H7N9 mutate to become easily transmitted between humans? We don’t know. But without sufficient supplies of a vaccine, we are not prepared to stop it.

The spread of antibiotic-resistant microbes also continues at an ever faster rate. Last year a comprehensive review predicted that, if left unchecked, drug-resistant infections will kill more people worldwide by 2050 than cancer and diabetes combined. Without a global effort led by the United States to halt the spread of this resistance and support for development of new antibiotics, we are in danger of returning to a pre-antibiotic world in which a cut could prove deadly and surgery would not be worth the risk of infection.

Yellow fever, a mosquito-borne disease that can kill up to 50 percent of those who get seriously sick, is on the cusp of a major outbreak in some of Brazil’s largest cities, while MERS — Middle East Respiratory Syndrome — continues to infect people on the Arabian Peninsula. If an effective vaccine is not developed, it will continue to be transmitted around the world and cause fatal outbreaks like the one that closed Samsung Medical Center in Seoul to new patients for weeks. A similar outbreak could occur at the Mayo Clinic or Johns Hopkins Hospital.