The human nasopharynx is frequently colonized by Streptococcus pneumoniae (the pneumococcus), serving as the reservoir for transmission, a state that necessarily precedes invasive pneumococcal infection. Influenza infection increases pneumococcal colonization density and dysregulates host immune responses, increasing the risk of secondary bacterial pneumonia and death (1–3).

Live attenuated influenza vaccine (LAIV) nasal spray has been used in the United States since 2003, and it has reduced severe influenza disease in the United Kingdom since its introduction in 2013 into the national pediatric immunization program. In mice, LAIV vaccination increases the density and duration of pneumococcal colonization (2) and rates of otitis media. In children, LAIV is associated with increased rates and density of bacterial colonization (4). Although LAIV is safe and not associated with increases in pneumococcal disease, these data suggest that it could increase pneumococcal transmission to susceptible individuals (5).