A single jab could protect against a wide range of pathogensIllustration: Timo LenzenTHE VITAL importance of vaccines is most apparent when they fall short. The covid-19 pandemic showed how quickly a new virus can spread while scientists race to catch up with jabs. Fast-evolving viruses can also evade existing protections. Each year’s flu vaccine is designed based on scientists’ best guess about which strains will dominate, given what was circulating the season before. In 2025 the H3N2 strain de...