Immunisation coverage and factors associated with incomplete immunisation in children under two during the COVID-19 pandemic in Sierra Leone

Abstract

Background: Routine childhood immunisation is one of the most important life-saving public health interventions. However, many children still have inadequate access to these vaccines and millions remain (partially) unvaccinated globally. As the COVID-19 pandemic disrupted health systems worldwide, its effects on immunisation have become apparent. This study aimed to estimate routine immunisation coverage among children under two in Sierra Leone and to identify factors associated with incomplete immunisation during the COVID-19 pandemic.

Methods: A cross-sectional household survey was conducted in three districts in Sierra Leone: Bombali, Tonkolili and Port Loko. A three-stage cluster sampling method was followed to enrol children aged 10-23 months. Information regarding immunisation status was based on vaccination cards or caretaker's recall. Using WHO's definition, a fully immunised child received one BCG dose, three oral polio vaccine doses, three pentavalent vaccine doses and one measles-containing vaccine dose. Following the national schedule, full immunisation status can be achieved at 9 months of age. Data were weighted to reflect the survey's sampling design. Associations between incomplete immunisation and sociodemographic characteristics were assessed through multivariable logistic regression.

Results: A total of 720 children were enrolled between November and December 2021. Full vaccination coverage was estimated at 65.8% (95% CI 60.3%-71.0%). Coverage estimates were highest for vaccines administered at birth and decreased with doses administered subsequently. Adjusting for age, the lowest estimated coverage was 40.7% (95% CI 34.5%-47.2%) for the second dose of the measles-containing vaccine. Factors found to be associated with incomplete immunisation status were: living in Port Loko district (aOR = 3.47, 95% CI = 2.00-6.06; p-value < 0.001), the interviewed caretaker being Muslim (aOR = 1.94, 95% CI = 1.25-3.02; p-value = 0.015) and the interviewed caretaker being male (aOR = 1.93, 95% CI = 1.03-3.59, p-value = 0.039).

Conclusion: Though full immunisation coverage at district level improved compared with pre-pandemic district estimates from 2019, around one in three surveyed children had missed at least one basic routine vaccination and over half of eligible children had not received the recommended two doses of a measles-containing vaccine. These findings highlight the need to strengthen health systems to improve vaccination uptake in Sierra Leone, and to further explore barriers that may jeopardise equitable access to these life-saving interventions.

Keywords: Childhood immunisation; Household survey; Routine immunisation coverage; Sierra Leone.

Fig. 1

Map of HHS districts in Sierra Leone

Fig. 2

Flowchart of the survey U2 = under two years of age ¹ To provide the list of clusters within project areas and the maps of the randomly selected clusters, Statistics Sierra Leone used information collected during the national census in 2015. Due to the year difference, two randomly selected clusters were no longer in the project areas and had to be substituted by back up clusters ² One initially recruited child was later excluded from the analysis, due to their recent relocation from Liberia to a survey cluster, which was not an exclusion criterion at the time of data collection. They had not followed the EPI schedule of Sierra Leone but instead had been vaccinated according to the slightly different program in Liberia, and therefore did not meet the study objectives

Fig. 3

Proportion of children aged 10–23 months vaccinated at any time before the survey^1,2 BCG = bacille Calmette-Guerin; Penta = pentavalent vaccine; IPV = inactivated polio vaccine; MCV = measles containing vaccine; OPV = oral polio vaccine ¹ Ordered following Sierra Leone’s EPI schedule ² MCV2: coverage among participants aged 16 months or older, allowing one month of delay