The Effects of LAIV on Nasopharyngeal Bacteria in Healthy 2-4 Year Olds: a Randomized Controlled Trial

Valtyr Thors, Hannah Christensen, Begonia Morales-Aza, Ian Vipond, Peter Muir, Adam H R Finn

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Rationale: Viral infections of the upper respiratory tract may influence the commensal nasopharyngeal bacteria. Changes in the bacterial niche could affect transmission dynamics. Attenuated vaccine viruses can be used to investigate this empirically in humans. Methods: We used trivalent Live Attenuated Influenza Vaccine (LAIV) to evaluate the effects of viral infection on bacterial carriage and density of S.pneumoniae, M.catarrhalis, H.influenzae and S.aureus. 151 healthy children were randomized 1:1 to receive the vaccine starting either at recruitment (n=74) or 28 days later (n=77) in a stepped wedge fashion, allowing comparisons between recipients and non-recipients as well as whole-group comparisons pre- and post- vaccination. Bacterial carriage and density were determined using qPCR assays. Measurement & Main Results: 151 children were recruited, 77 in the LAIV group and 74 controls. LAIV recipients (n=63 analysed) showed an apparent transient increase in H.influenzae carriage but no further significant differences in carriage prevalence of the four bacterial species compared to controls (n=72 analyzed). S.pneumoniae density was substantially higher in vaccine recipients (16687 vs 1935 GC/ml) 28 days after the first dose (p<0.001). Whole-group multivariable analysis (pre-vaccine, after one dose and after two doses) also showed increases in density of other species and H. influenzae carriage prevalence. Conclusion: In the absence of any safety signals despite widespread use of the vaccine, these findings suggest that bacterial density and thus, transmission rates amongst children and to other age groups may rise following attenuated influenza infections without associated clinical disease. LAIV could therefore be used as an experimental tool to elucidate the dynamics of transmission of nasopharyngeal bacteria.
Original languageEnglish
Pages (from-to)1401-1409
Number of pages9
JournalAmerican Journal of Respiratory and Critical Care Medicine
Issue number12
Early online date7 Jan 2016
Publication statusPublished - 15 Jun 2016


  • Bacterial colonization
  • Live attenuated influenza vaccine
  • Bacterial density
  • Children


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