Flu viruses come in two versions, influenza A and influenza B. To public health officials, influenza B viruses are less alarming than influenza A strains because they circulate largely in humans, which means they do not have the animal reservoirs that are necessary to cause a pandemic. But they do play an important part in the annual flu. Scientists from the Dutch Crucell Vaccine Institute and the Scripps Research Institute have identified three broadly neutralizing antibodies to influenza B viruses.