A cholera vaccination in Malawi. ©WHOWHO’s contributors are supporting the “Big Catch-Up” – a push to get countries back on track with vaccinations after disruptions brought on by the COVID-19 pandemic, natural disasters and armed conflicts.WHO estimates that 25 million children missed out on vaccination in 2021, six million more than in 2019 and the highest number since 2009.To mark World Immunization Week (24-30 April), we visit campaigns to stop flood-related cholera outbreaks in Kenya, Malawi, and Mozambique; polio and measles campaigns in Syria in the aftermath of a massive earthquake; and the quest to reach “zero-dose” children caught in Somalia’s years-long drought.This issue celebrates vaccination successes in Africa, where a grant from the European Union helped push a group of countries with very low COVID-19 vaccination coverage closer to, or in some cases above, the continent’s average.Also read about stopping COVID-19 in the Americas, HPV vaccination to end cervical cancer in Sierra Leone, Montenegro’s Health Caravan project and work to vaccinate vulnerable people ahead of Lao PDR’s National Games.Also see:All about World Immunization Week 2023New cholera cases in Africa surging fast, reach a third of 2022 total in a month Polio and measles vaccinations are deployed in Syria’s earthquake zonesThis month’s polio and measles vaccination campaign comes a month after a drive that administered cholera vaccine to nearly 1.7 million people. ©WHOThis month, WHO and partners are working to administer polio and measles vaccinations to 800 000 small children in the northwest of the country where a February earthquake damaged or destroyed 67 health facilities.The 10-day campaign involves about 3 000 health workers, many