Table 1

Potential studies to investigate reduced LAIV VE hypotheses

HypothesesStudy approaches
CDC/DoD A/H1N1pdm09 specific finding — related to chance, methodology, programmatic issuesMore highly powered vaccine effectiveness study with larger sample size in eligible population also allowing for stratification by age and/or previous exposure
Replicative fitness of the current A/H1N1pdm09 strainComparative shedding study of LAIV vaccinees to compare different vaccine virus formulations
Viral interference/competition between A/H1N1pdm09 vaccine strain and other vaccine viruses in multivalent formulationIn vitro and vivo challenge studies to compare viral shedding patterns
Prior vaccination with LAIV or IIV resulting in specific immunological interference with H1N1pdm09 vaccine virus replicationVE and shedding studies to compare groups with different prior vaccine exposure
Repeat LAIV vaccination resulting in broader, longer term immunological changes affecting all viruses (mimicking adult response)Serological and cell-mediated LAIV immunity studies
  • CDC, Centers for Disease Control and Prevention; DoD, Department of Defence; IIV, inactivated influenza vaccine; LAIV, live attenuated influenza vaccine; VE, vaccine effectiveness.