Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Immunisation is a key component in the prevention of illness and the Cochrane review of interventions to improve coverage of childhood immunisation in low- and middle-income countries was updated for the second time in December 2023. We asked lead author, Angela Oyo-Ita from University of Calabar Teaching Hospital in Nigeria, to tell us about the latest findings in this podcast.

Angela: Low- and middle-income countries, which I'll call LMICs for short, bear the greatest burden of childhood illness and death; mostly from infectious diseases. Immunization plays a major role in reducing morbidity and mortality from these diseases and it has been estimated that the traditional Expanded Program on Immunisation, or EPI, vaccines, which was launched in 1974, prevent 2.5 million child deaths every year; mainly from measles, pertussis, tetanus, and diphtheria. They also prevent severe morbidity for millions more children around the world from devastating diseases such as poliomyelitis, tuberculous, and meningitis.
Immunisation has the potential to do more. Increasing coverage with existing vaccines, as well as the introduction and increased uptake of a portfolio of newly available vaccines in EPI programmes in LMICs, could save the lives of millions more children each year.
However, despite global improvements in vaccine uptake, progress in LMICs is slow. It is yet to reach the optimal target and getting children immunized in LMICs remains a challenge. For example, about two-thirds of the 19 million children under 1 year of age who have not received the diphtheria, tetanus toxoid and pertussis, or DPT3, immunisation live in 10 LMICs. Evidence is required to inform strategies to reach partially vaccinated and unvaccinated people in these, and other LMICs.
To help with this, we reviewed research into strategies that could boost the proportion of children who receive DTP3/Penta 3 by one year of age and the proportion who receive all recommended vaccines by the age of two. We also looked for the effect on other outcomes, but there was insufficient evidence for most of them.
We found 41 studies, that had recruited a total of just over 100,000 children. These were in four upper-middle-income countries (China, Georgia, Mexico, Guatemala), 11 lower-middle-income countries (Côte d'Ivoire, Ghana, Honduras, India, Indonesia, Kenya, Nigeria, Nepal, Nicaragua, Pakistan, Zimbabwe), and three lower-income countries (Afghanistan, Mali, Rwanda). However, there is still a considerable need for new, rigorous studies of low risk of bias to strengthen the evidence base.
Eleven interventions were either as standalone or combined interventions, and we grouped the interventions as recipient, health provider, health system or community oriented.
In summary, we found evidence that recipient-oriented interventions such as health education and home-based records may improve DTP3 uptake. Of the several health system-oriented interventions studied, the evidence indicated that integration of immunization services with other services may improve DTP3 uptake. Also, immunization outreach, either as a standalone or in combination with health education or a non-monetary incentive, probably improves full vaccination of under 5s. We are uncertain of the effect of health provider intervention (specifically, supportive supervision) on vaccine uptake but a combination of involving community leaders and training of health providers may improve uptake of DTP3 and measles vaccination.

Mike: Thanks Angela. If you'd like to read the full version of this review, it's available open access from Cochrane Library dot com with a simple search for 'improving coverage of childhood immunisation'.