[Correspondence] Safeguarding immunisation: a core function of WHO

Vaccination remains the most cost-effective public health intervention, preventing millions of deaths and reducing disease burden worldwide.1 However, their impact is rendered meaningless if vaccines are not epidemiologically relevant to the populations they serve, are not accepted by communities, or are not effectively delivered through routine or mass immunisation programmes. As history has shown, immunisation programmes have always faced threats—from political instability to misinformation—and these challenges are growing more severe in today's global landscape.