Abstract
Streptococcus pneumoniae (Sp) is a leading cause of pneumonia, meningitis and sepsis. Interruption of transmission of vaccine serotypes underlies effectiveness of pneumococcal conjugate vaccine programmes at population level. However, factors driving pneumococcal transmission remain poorly understood. Sp nasal colonisation is common in young children, its density varies widely, and higher levels are associated with respiratory viral infections, yet the relationship between density and infectiousness is unclear.The live attenuated influenza vaccine (LAIV) is provided to young children in the United Kingdom, offering protection against influenza and indirectly protecting the wider community. Research indicates that LAIV can increase Sp carriage density in vaccinated children. This thesis aimed to evaluate factors influencing Sp transmission, specifically, the impact of LAIV, as a viral proxy, and carriage density on transmission to close contacts.
A randomised controlled study involving 405 two-year-old children and 958 household contacts was conducted across 10 sites in the UK. Nasopharyngeal swabs were collected from all participants during five visits every two weeks and tested for Sp carriage. LAIV was administered to 205 children at the first visit and 200 children at the third visit. The study compared density and transmission rates between the vaccinated and unvaccinated groups, using regression models to analyse their associations.
At two weeks, a greater proportion of vaccinated children continued to be Sp colonised, with increased densities compared with controls and the rates of Sp transmission to their household contacts was increased 2.1-fold. Post hoc analyses showed that higher density was associated with Sp transmission, independently of LAIV. These findings indicate that measures aimed at curbing respiratory viral infections may play a key role in reducing upper airway bacterial transmission and thereby disease. Important knowledge gaps in understanding Sp transmission and the bacterial-viral relationship call for further investigation.
| Date of Award | 30 Sept 2025 |
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| Original language | English |
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| Supervisor | Adam H R Finn (Supervisor), Robin Marlow (Supervisor), Leon Danon (Supervisor) & Fernanda Rodrigues (Supervisor) |