The world is facing a red alert for children's health: Vaccination coverage dropped sharply during the COVID-19 pandemic, leaving millions more children unprotected against some of childhood's most serious diseases. In addition, many millions of children from some of the world's most marginalised communities have long missed out on life-saving vaccination. Catch-up and recovery are needed urgently to vaccinate the children missed and to avoid further backsliding. And greater effort is needed to reach the children historically left behind. The State of the World's Children 2023 examines what needs to happen to ensure that every child, everywhere is protected against vaccine-preventable diseases