The COVID-19 pandemic created gaps in immunization coverage and vaccine preventable disease (VPD) surveillance which required specific and urgent attention. Failure in sustaining or revitalizing immunization services and insufficient catch-up vaccination bears the risk of VPD emergence resulting in increased childhood morbidity and mortality and putting VPD control and elimination goals at risk. There was an urgent need for ongoing assessments of immunization programme recovery, catch-up vaccination strategy implementation for vulnerable populations, and ensuring vaccine coverage equity and health system resilience.

Despite the efforts made by countries to sustain routine immunization service delivery, the pandemic-associated disruptions and COVID-19 vaccination efforts strained systems in 2020 and 2021. Thus, the regional coverage of 3 doses diphtheria, tetanus, pertussis containing vaccine (DTP3; as pentavalent vaccine formulation in the South-East Asia Region of the World Health Organization [WHO]) decreased from 91% in 2019 to 85% in 2020 and to 82% in 2021. The number of children who did not receive the first dose of DTP vaccine ("zero-dose children"1) increased from 2 million in 2019 to 4.6 million in 2021.

The pandemic impact was though not universal. Based on DTP3 coverage, the number of zero-dose children, and district-level variability in coverage in 2020 and 2021, countries in the Region could be divided into three groups; namely those that maintained high DTP3 coverage, countries that faced a decline in DTP3 coverage in 2020 but stabilized/ showed recovery trends in 2021 and those with continued decline in DTP3 coverage. Despite monthly immunization achievements reported in 2022 showing further coverage recovery, still many children were unimmunized or under-immunized.