January 2018 marked the centennial of the 1918 influenza worldwide pandemic, which served as a stark reminder that the need for a universal influenza vaccine is paramount. Jaime Polychrones at Clarivate Analytics outlines how more than 100 years after the deadliest influenza outbreak in modern history – one that killed one-fifth of the world’s human population – there is still no vaccine available to protect people from most or all strains of influenza each influenza season.