Time series analysis of routine immunisation coverage during the COVID-19 pandemic in 2021 shows continued global decline and increases in Zero Dose children

Whilst it is now widely recognised that routine immunisation (RI) was disrupted by the COVID-19 pandemic in 2020 compared to previous immunisation performance, the extent of continued interruptions in 2021 and/or rebounds to previous trends remains unclear, with sporadic surveys reporting signs of immunisation system recovery at the end of 2020. We modelled country-specific RI trends using validated estimates of national coverage from the World Health Organisation and United Nation Childrens Fund for over 160 countries, to project expected diphtheria, tetanus, and pertussis-containing vaccine first-dose (DTP1), third-dose (DTP3) and measles-containing vaccine first-dose (MCV1) coverage for 2021 based on pre-pandemic trends (from 2000-2019). We estimated a 3{middle dot}6% (95%CI: [2{middle dot}6%; 4{middle dot}6%]) decline in global DTP3 coverage in 2021 compared to 2000-2019 trends, from an expected 90{middle dot}1% to a reported 86{middle dot}5% across 164 reporting countries, and similar results for DTP1 (2{middle dot}8% decline; 95%CI: [2{middle dot}0%; 3{middle dot}6%]), and for MCV1 (3{middle dot}8% decline; 95%CI: [4{middle dot}8%; 2{middle dot}7%]). 86{middle dot}5% global coverage in 2021 represents a further decrease from that reported in 2020 and 2019, and translates to a 16-year setback in RI coverage, i.e., 2005 levels. Hypothesised and early signals of rebounds to pre-pandemic coverage were not seen in most countries. The Americas, Africa, and Asia were the most impacted regions, with low- and middle-income countries the most affected income groups. The number of Zero Dose children also continued to increase in 2021. DTP1 coverage declined worldwide from an expected 93{middle dot}7% to a reported 90{middle dot}9% (2{middle dot}8% decline; 95%CI: [2{middle dot}0%; 3{middle dot}6%]) which translates into an additional 3.4 million Zero Dose children on top of an expected 11.0 million (30.9% increase) at the global level. We hope this work will provide an objective baseline to inform future interventions and prioritisation aiming to facilitate rebounds in coverage to previous levels and catch-up of growing populations of under- and un-immunised children.