The aim of this study is to assess the impact of a mass campaign with a single, fractional dose of Pneumosil®, a PCV10, on VT carriage. A 20% fractional dose (1/5th) will be used as a practical formulation to prepare and administer. This study will assess whether the impact of a single fractional dose mass campaign on carriage is non-inferior to a single full dose mass campaign in a cluster randomized trial in a low coverage setting in Niger. The results would provide evidence of the population-level direct and indirect impact of fractional dose in older children which will be completed by mathematical modelling, to inform the policy debate regarding PCV dosing schedules in different contexts. This trial and the modelling exercises that follow, would allow for larger scale evaluation of fractional dose PCV strategies in multiple contexts.

In 2015, there were an estimated 8.9 million cases (uncertainty range 7.7-10.6 million) of clinical pneumococcal pneumonia globally, with 2.4 million cases estimated in Africa alone (uncertainty range 2.1-3.1 million). These figures represent a global reduction of 37% from 14.2 million cases (12.3 million-16.9 million) in 2000. However, pneumococcal disease continues to be a leading cause of severe disease and death representing 10% of all death in children under 5 years of age (1). These deaths occur disproportionally in low- and middle-income countries (LMICs), with approximately 50% of global pneumococcal deaths estimated to occur in 4 countries: India, Nigeria, Pakistan and the Democratic Republic of Congo.

Vaccination campaigns targeting children up to 5 years of age have an effect in the reduction of VT carriage disease. However, in crises or settings with high prevalence of malnutrition, the high pneumococcal carriage prevalence is likely to extend to older age groups. Single dose vaccination of a larger age group might be needed to control VT circulation. Currently, for GAVI-supported countries such as Niger, PCV13 vaccine has a cost of US$3 per dose. Pneumosil®, a PCV10 manufactured by Serum institute of India Ltd has the lowest price of all WHO prequalified vaccines, at US$2 per dose.

Mass campaigns targeting large groups require many doses and might not be sustainable over time. Fractional doses of PCV could be a solution to overcome the high PCV costs, increase vaccine access and expand vaccination benefits through alternative strategies. The study population (ages 1-9) stems from an LSHTM modelling study.

Objectives of the study Primary objective: evaluate whether the full dose of PCV is superior to the absence of vaccine and then if a single 20% dose of PCV is non-inferior to a full dose in carriage reduction.

Secondary objectives:

• To measure the age-stratified prevalence of NP carriage of S. pneumoniae in children 1-9 years of age in the study area.
• To determine the impact of a mass vaccination campaign with one full dose of PCV in children 1 to 9 years of age on VT pneumococci carriage 6 months after vaccination
• To assess the occurrence of adverse events (AE) and serious adverse events (SAE) during 28 days after administration of fractional and full doses and SAEs throughout the duration of follow-up
• To model the potential impact of fractional dose PCV campaigns in other contexts using the results of the clinical trial.
• To develop recommendations on how a potential future fractional dose PCV mass campaign could be successfully planned, communicated, delivered, and integrated into national immunization programmes using qualitative analysis.

Note: the 1-9 years age group targeted for the mass campaign is based on data from a model in Kilifi, Kenya. Baseline carriage survey data together with data will be used on interactions between age groups and PCV coverage data collected during the baseline survey, to estimate the age group that should be targeted for vaccination.

Methodology A cluster-randomized, blinded, non-inferiority trial will be implemented in rural villages of the Madarounfa District of Niger. Clusters will be randomized to full dose, fractional dose or control arm in 2:2:1 allocation ratio. Clusters will be composed of a village or group of neighbouring villages that share a school or market. Stratified randomization will be used to consider size of clusters and proximity to health centre. Vaccination will target all children aged approximately 1 to 9 years of age residing in the selected villages Prior to the mass vaccination campaign, a cross-sectional survey will be implemented to estimate community-level carriage of VT pneumococci, as well as to collect data on household composition, social interactions and PCV vaccination coverage.

For participation in pneumococcal carriage surveys:

Inclusion criteria:

1. Aged 1-9 years
2. Residing in the villages included in the study
3. Parent or caretaker provides informed consent for the child to participate in the study

Exclusion criteria:

1. Head or facial injuries that contraindicate nasopharyngeal swabbing
2. Any condition or criteria, including acute or chronic clinically significant abnormality that in the opinion of the investigator might compromise the wellbeing of the participant or interfere with the outcome of the study

For participation in mass vaccination campaigns (with full or fractional dose PCV10)

Inclusion criteria:

1. Aged 1-9 years
2. Residing in the villages included in the study and allocated to vaccination
3. Head of the household or main caretaker provides consent for the child to be vaccinated

Exclusion criteria:

1. Hypersensitivity to any component of the vaccine, including diphtheria toxoid
2. Vaccination with a PCV vaccine within the previous 4 weeks, as there should be a minimum of 4 weeks between doses
3. Moderate or severe febrile illness (temperature ≥39°C) is a temporal contraindication and the child should not be vaccinated until improvement
4. Any condition or criteria, including acute or chronic clinically significant abnormality that in the opinion of the clinical staff might compromise the wellbeing of the volunteer

IPD will consist of sociodemographic data collected in baseline and post-vaccination surveys, as well as results of pneumococcal isolation and serotyping.

De-identified IPD will be available after final data collection and cleaning, and once laboratory quality control procedures have been conducted.

Any interested party may request access to the data for the purposes of secondary analysis or meta-analysis. The process for requesting data, and the criteria upon which requests will be judged are described in Epicentre Standard Operating Procedures.

Adverse event data were collected for 28 days following vaccination.

Population under surveillance for adverse events is the total population aged 1-9 living in the 63 clusters.

Vaccinators will not be blinded, but participants will not know vaccine dosage allocation. Laboratory staff (outcome assessors) will be blinded to their group allocation.