Generating evidence on optimal vaccination strategies to protect children in humanitarian settings against pneumococcal pneumonia
Vaccinating children with pneumococcal conjugate vaccine
Pneumococcal conjugate vaccine (PCV) can provide significant protection against pneumococcal disease within displaced populations. Delivering PCV through existing mass vaccination campaigns to children under five years of age offers substantial population-level benefit when vaccination uptake is high.
Campaigns that include only those children at highest risk (i.e. children under two years) are less effective, and less efficient than vaccinating children under five years. When vaccine uptake is high, protection against pneumococcal infection may be conferred to children born following the vaccination campaign via herd protection. Herd immunity may sustain protection for up to three years.
Background
Pneumococcal pneumonia is a leading cause of death amongst children worldwide. Displaced populations often experience: high prevalence of malnutrition, crowded living conditions, limited access to curative care, and disrupted routine immunisation services. These health threats put displaced populations at particularly high risk of pneumococcal infection.
The Evaluating Strategies for Pneumococcal Immunisation Campaigns in humanitarian Crises (ESPICC) study aimed to estimate the effectiveness of strategies for delivering pneumococcal vaccines on the health of children living in a camp for internally displaced people (IDP) in Somaliland.
How the research was conducted
We carried out a population-representative, cross-sectional, nested risk factor and pneumococcal carriage survey in Digaale IDP camp. The team then used mathematical modelling to simulate the effect of a single-dose PCV vaccination campaign in Digaale, and other crises-affected populations.
Key findings
Based on data collected from 509 participants across 464 households (representing 65% of inhabited shelters) we found:
- A high prevalence of risk factors for respiratory illness (e.g. crowded living conditions, and 20% of children under five years were stunted)
- A high disease burden (i.e. self-reported, recent pneumonia in 46% of children, high crude death rates, and high pneumococcal carriage rates similar to those of rural Kenya)
- Age groups driving transmission (i.e. exposure to pneumococci in children under five was primarily due to contact with carriers aged two to 14 years)
- Evidence of optimal vaccination strategy (i.e. restricting vaccination to children under two years had limited and short-lived effects; however, high-coverage vaccination of all children under five years could prevent about 30% of severe pneumococcal disease in the two years following a vaccination campaign)
- Additional benefits of vaccinating children under five years (i.e. high-coverage PCV vaccination of children under five reduces transmission - thereby generating indirect protection to unvaccinated infants born after the campaign - and is the most efficient use of vaccine)
- Benefits of vaccinating children older than five years of age (i.e. when migration rates are high, or PCV vaccine coverage is low, extending campaigns to include older children can sustain indirect protection)
- Benefit of a single-dose campaign (i.e. not only are single-dose campaigns more feasible to implement operationally, it is also more effective to give a single-dose to a wider group of children, than two doses to a narrower group of children)
Implications for humanitarian practitioners and policymakers
Our findings suggest that humanitarian practitioners should consider integrating PCV for children under five years of age into their routine humanitarian response portfolio. This could be done in the acute phase of a humanitarian crisis through co-delivery with measles-containing vaccines and vitamin A.
A PCV campaign should not be limited to children who are at the greatest risk of severe disease (i.e. children under two years). To be maximally impactful, PCV campaigns should also include key transmitters; namely, children aged two to 10 years. Campaigns that target only those children most at risk are less effective and less efficient when it comes to offering durable protection.
Recommendations for future research
Future research should investigate the value of repeated vaccination campaigns when routine immunisation services cannot be reinstated by the time protection from the initial campaign has waned.
A demonstration implementation study is currently ongoing to further substantiate the predictions of our mathematical model. Results are expected in early 2025.
The study team
London School of Hygiene & Tropical Medicine: Kevin van Zandvoort; Francesco Checchi; Catherine R McGowan; Abdihamid Warsame; Olivier le Polain; Rosalind M Eggo; Anna Carnegie; Stefan Flasche
Save the Children Somaliland: Mohamed Bobe; Mohamed Abdi; Saed Ibrahim; Mohamed Egeh; Binyam Gebru; Mohamed Magan; Mohamed Saed; Mohamed Kahow
Somaliland Ministry of Health Development: Abdirahman I Buqul; Mohamed A Hergeeye; Saeed M Soleman; Mohamed Y Warsame
Save the Children UK: Rachael Cummings; Emma Diggle; Olimpia de la Rosa
Murdoch Children's Research Institute: Catherine Satzke; Casey Pell; Kim Mulholland
Médecins Sans Frontières UK: Bhargavi Rao; Ruby Siddiqui; Kartini Gadroen
Keywords
pneumococcal disease; pneumonia; vaccination; children; refugees; humanitarian response