In a report earlier this summer, the Joint Committee on Vaccinations and Immunisations (JCVI) noted there could be a 50% increase in cases of influenza in comparison to other years. Madeleine Finlay speaks to Ian Sample about the factors at play, from weakened immunity to the expanded vaccine programme, and hears from Derek Smith, professor of infectious disease informatics about how the World Health Organization has decided on which influenza strains to vaccinate against this year. Help support our independent journalism at theguardian.com/sciencepod