Zero-dose children and the extended immunisation cascade: Understanding the path to full immunisation with six childhood vaccines in 43 countries.

Background: As part of the Immunisation Agenda 2030, the World Health Organization set a goal to reduce the number of children who did not receive any routine vaccine by 50% by 2030. We aimed to describe the patterns of vaccines received for children with zero, one, and up to full vaccination, while considering newly deployed vaccines (pneumococcal conjugate vaccine (PCV) and rotavirus (ROTA) vaccine) alongside longstanding ones such as the Bacille Calmete-Guérin (BCG), diphtheria, tetanus, and pertussis (DPT), and poliomyelitis vaccines, and measles-containing vaccines (MCVs).

Methods: We used data from national household surveys (Demographic and Health Surveys and Multiple Indicator Cluster Surveys) carried out in 43 low- and middle-income countries since 2014. We calculated the immunisation cascade as a score ranging from zero to six, considering BCG, polio, DPT, and ROTA vaccines, and the MCV and PCV. We also described the most prevalent combination of vaccines. The analyses were pooled across countries and stratified by household wealth quintiles.

Results: In the pooled analyses with all countries combined, 9.0% of children failed to receive any vaccines, 58.6% received at least one dose of each of the six vaccines, and 47.2% were fully vaccinated with all doses. Among the few children receiving 1-5 vaccines, the most frequent were BCG vaccines, polio vaccines, DPT vaccines, PCV, ROTA vaccines, and MCV.

Conclusions: Targeting children with their initial vaccine is crucial, as those who receive a first vaccine are more likely to undergo subsequent vaccinations. Finding zero-dose children and starting their immunisation is essential to leaving no one behind during the era of Sustainable Development Goals.