# Pneumococcal Carriage Among Children and Adults Before and After a Change from a Three-dose 13-valent Pneumococcal Conjugate Vaccine Schedule without a Booster to a Two-Dose Schedule with a Booster in Burkina Faso

## TL;DR

This study examines pneumococcal carriage in Burkina Faso before and after changing the PCV13 vaccine schedule, finding a significant decline in infants but not in other age groups.

## Contribution

The study evaluates the impact of a PCV13 schedule change on pneumococcal carriage in different age groups in Burkina Faso.

## Key findings

- PCV13-type carriage declined significantly among infants from 2020 to 2023.
- The decline in infants is likely unrelated to the booster dose, as only those aged ≥9 months could have received it.
- Additional birth cohorts are needed to assess the long-term effects of the new vaccine schedule.

## Abstract

In June 2021, Burkina Faso changed the 13-valent pneumococcal conjugate vaccine (PCV13) schedule from three primary doses with no booster (at 2, 3, 4 months) (3+0) to two primary doses with a booster (at 2, 4, 9 months) (2+1), which may optimize vaccine impact due to a booster dose.

We conducted two cross-sectional, age-stratified (age 1–11 months [infants], 1 year, 2–4 years, 5–14 years, and ≥15 years) pneumococcal carriage surveys in Bobo-Dioulasso in April–May 2022 and March–April 2023 and compared results with one similar survey conducted in March 2020. We collected demographic and epidemiologic information, including vaccination history (participants aged <5 years), and one nasopharyngeal (all participants) and one oropharyngeal (participants aged ≥5 years) swab from participants. Pneumococci isolated by culture were serotyped by PCR (all isolates in 2020 and 2022) and/or Quellung (subset of isolates in 2020 and 2022, all isolates in 2023). We evaluated pneumococcal carriage before (2020), during transition (2022), and after (2023) the PCV13 schedule change.

We enrolled 1,002, 1,025, and 1,007 participants in 2020, 2022, and 2023, respectively. Median age at dose 3 for 2+1-eligible children (infants in 2022 and children aged <2 years in 2023) was 4.3 months in 2022 and 9.1 months in 2023. From 2020 to 2023, PCV13-type carriage declined significantly among infants (2023: 9.5% 2020: 19.0%; adjusted prevalence ratio: 0.53, 95% CI: 0.31–0.88) but not in other age groups.

The decline in PCV13-type carriage observed only in infants is likely unrelated to the PCV13 schedule change, since only those aged ≥9 months could have received a booster dose. Additional birth cohorts vaccinated with the 2+1 schedule are needed to understand the effects on PCV13-type carriage.