We all have tiny hairs inside of our ears, and these hairs are doing important work: they convert sounds into electrical signals that can be interpreted by the brain. If these hairs are not doing what they need to do, deafness is the result, and this problem is behind roughly half of cases of hearing loss in early life. Now, scientific teams in the US and Switzerland have developed a genetically modified virus that could infect these hair cells and correct the error. Their work was tested on deaf mice, and injections of the virus into their ears led to a substantial improvement in hearing. The scientists think that this new therapy to treat hereditary deafness in humans could be available within five years.