H5N1 vaccine update

Moderna has started a Phase 3 trial of its mRNA H5 bird flu vaccine, with first doses already given in the UK and the U.S. (nihr.ac.uk) The study will test mRNA-1018 in about 4,000 adults age 18 and older, with roughly 3,000 participants recruited in the UK and the rest in the U.S. The trial is sponsored by Moderna, backed by the National Institute for Health and Care Research, and run through the company’s UK government partnership managed by the UK Health Security Agency. (nihr.ac.uk) Messenger RNA vaccines work by giving the body genetic instructions to make a harmless piece of a virus, so the immune system can practice spotting it before a real infection. This Phase 3 trial is checking safety and immune response, not whether the shot prevents disease in a live outbreak. (sciencemediacentre.org) H5N1 still does not spread easily between people, and the U.S. Centers for Disease Control and Prevention says there is no known person-to-person spread at this time. The agency still lists the current public health risk as low. (cdc.gov) Health agencies are moving faster on vaccines because the virus has spread widely in birds and has also turned up in mammals, including U.S. dairy cows. The National Institute for Health and Care Research said 116 confirmed human cases had been reported worldwide since 2024 when it announced the trial on April 22. (nihr.ac.uk) In the U.S., the Centers for Disease Control and Prevention now counts 71 human H5 cases since 2024, including two deaths. Its breakdown lists 41 cases tied to dairy herds, 24 to poultry farms or culling operations, three to other animal exposures, and three with no identified source. (cdc.gov) The vaccine push is landing as Cambodia reported its fourth human H5N1 case of 2026 on April 22. Cambodian authorities said a 66-year-old woman from Trapaing Thkov village in Svay Rieng province tested positive on April 21 and was hospitalized after investigators found sick and dead chickens in her village and at her home. (bnonews.com) Cambodia’s response teams are tracing contacts and giving close contacts oseltamivir, sold as Tamiflu, under the country’s standard protocol. BNO News reported Cambodia recorded 19 human H5N1 cases in 2025, eight of them fatal. (bnonews.com) Global health agencies have been warning about the same pattern for months: a virus that remains mainly an animal disease, but keeps finding new hosts and new chances to infect people. Moderna’s late-stage trial is an attempt to have a human shot further along before that pattern changes. (who.int)