Figure 1: The immunisation cascade In the 92 countries, 7.7% were in the zero-dose group, and 3.3%, 3.4% and 14.6% received one, two or three vaccines, respectively; 70.9% received the four types and 59.9% of the total were fully immunised with all doses of the four vaccines. Three-quarters (76.8%) of children who received the first vaccine received all four types.
How do children move from zero-dose to full coverage? That was the main question for Bianca Cata-Preta and her research colleagues. The data analyses show the importance of focusing on zero-dose children because those who are reached with the first vaccine are highly likely to also receive the remaining vaccines.
The researchers analysed national representative data from Demographic and Health Surveys (DHS) and Multiple Indicator Cluster Surveys (MICS) conducted in 92 low and middle-income countries between 2010 and 2019, including Bangladesh. Information on the immunisation status of children aged 12-23 months was extracted from vaccination cards, or otherwise from the mothers’/caregivers’ report, considering four routine vaccines: BCG, polio (OPV/IPV), DPT and measles-containing vaccines (MVC).
The research focuses on the prevalence of zero-dose children and on the immunisation cascade, i.e. how children advance from zero to full immunisation, analysing the progress from one vaccine to two, three and then four vaccines, without looking at the number of doses. The research also analyses the pathway to full coverage.
The research presents data for all 92 countries and for three country income groups (low, lower-middle and upper-middle income). Analyses are also presented for the poorest-wealthiest quintile, and stratified by sex and rural-urban residence. The average zero-dose prevalence was 7.7%, ranging from 11.1% in low-income countries to 5.2% in upper-middle-income countries. Zero-dose children were more frequently found in rural than in urban areas and in poorer households. There were sharp inequalities according to household wealth: in the poorest quintile, the zero dose prevalence was three times higher compared to in the wealthiest quintile, respectively 12.5% and 3.4%. There were no consistent differences between boys and girls.
Looking at the country-wise immunisation data, the performance of Bangladesh as a lower-middle income country, was significantly better with a national zero-dose prevalence of just 2.2% according to the used DHS 2014 source data. While inequalities according to household wealth are clearly notable, the prevalence of the poorest quintile (3.5%) in Bangladesh is on the same level as the average wealthiest quintile for all researched countries but it is almost zero for the wealthiest quintile (0.2%). Contrary to the global trend, zero-dose children are less frequently found in rural Bangladesh than in its urban areas.
The immunisation cascade data analyses show that being zero dose is more common than receiving at least one dose of exactly 1 or 2 vaccines; in other words, most children tend to be either zero doses or receive at least the first dose of 3 or more vaccines. This suggests that moving children out of the zero-dose state is a particularly critical point in ensuring the entire population is fully immunised.