Maternal pneumococcal nasopharyngeal carriage and risk factors for neonatal carriage after the introduction of pneumococcal conjugate vaccines in The Gambia.

OBJECTIVES

Pneumococcal nasopharyngeal carriage occurs early in life. However, the role of vertical transmission is not well understood. The aims of this study were to describe carriage among mothers and their newborns, and to assess for risk factors for neonatal carriage.

METHODS

In a nested retrospective cohort study, we analysed data from the control arm of a randomized controlled trial conducted in The Gambia 2 to 3 years after introduction of pneumococcal conjugate vaccine (PCV) 13. Nasopharyngeal swabs were collected from 374 women and their newborns on the day of delivery, then 3, 6, 14 and 28 days later. Pneumococci were isolated and serotyped using conventional microbiologic methods.

RESULTS

Carriage increased from 0.3% (1/373) at birth to 37.2% (139/374) at day 28 (p <0.001) among neonates and from 17.1% (64/374) to 24.3% (91/374) (p 0.015) among women. In both groups, PCV13 vaccine-type (VT) serotypes accounted for approximately one-third of the pneumococcal isolates, with serotype 19A being the most common VT. Maternal carriage (adjusted odds ratio (OR) = 2.82; 95% confidence interval (CI), 1.77-4.80), living with other children in the household (adjusted OR = 4.06; 95% CI, 1.90-8.86) and dry season (OR = 1.98; 95% CI, 1.15-3.43) were risk factors for neonatal carriage. Over half (62.6%) of the neonatal carriage was attributable to living with other children in the same household.

CONCLUSIONS

Three years after the introduction of PCV in The Gambia, newborns are still rapidly colonized with pneumococcus, including PCV13 VT. Current strategies for pneumococcal control in Africa do not protect this age group beyond the herd effect.