Despite the global disease burden of Streptococcus pneumoniae (Sp), factors determining Sp transmission have not been fully evaluated. Substantial evidence supports that upper respiratory tract (URT) pneumococcal colonisation sustains population based transmission (1,2) and Sp transmission requires close proximity (1). Young children are most likely the main reservoir and transmission drivers of Sp: they carry Sp at highest rates, particularly if attending daycare; carers of young children carry Sp at higher rates than non carer adults of similar age; and high vaccination coverage against Sp in early childhood with pneumococcal conjugate vaccines (PCV) reduces vaccine type disease and carriage in the whole population (3,4). There have been few studies evaluating household Sp transmission and, to our knowledge, none investigating the impact of Sp density on household transmission. The intranasal LAIV is offered every autumn in the UK childhood immunisation programme to children aged 2 years and over. LAIV provides effective protection against influenza for those vaccinated and indirect protection for the wider community (5). LAIV has also been shown to increase Sp carriage density in mice and, to a limited degree, in children (6, 7, 8). This attenuated upper respiratory tract (URT) infection can therefore be used to investigate whether increases in Sp density in carriers augment transmission to their contacts. We conducted a randomised controlled trial to assess the impact of LAIV administration on Sp carriage density in previously LAIV naive 2 year old children and onward transmission to their household contacts.

Brad Gessner is an employee of Pfizer holds stock in the company.

ISRCTN10720581

This study was funded by the Bill & Melinda Gates Foundation and Pfizer. I received a fellowship from the European Society of Paediatric Infectious Diseases

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Ethical and governance approvals were granted by the UK Research Ethics Committee (Cambridgeshire and Hertfordshire) (17/EE/0351) and Health Research Authority

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

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All data produced in the present study are available upon reasonable request to the authors