We randomized 115 children to trivalent inactivated influenza vaccine (TIV) or placebo. Over the following 9 months, TIV recipients had an increased risk of virologically-confirmed non-influenza infections.
TIV recipients may lack temporary non-specific immunity that protected against other respiratory viruses.
We investigated the incidence of acute upper respiratory tract infections (URTIs)… in a randomized controlled trial of influenza vaccination.
We defined the follow-up period for each participant from 14 days after receipt of TIV or placebo to collection of midstudy serum samples as the winter season and from collection of midstudy samples through final serum sample obtainment as the summer season.
We defined an acute respiratory illness (ARI) determined by self-reported signs and symptoms as ≥2 of the following signs or symptoms: body temperature ≥37.8°C, headache, sore throat, cough, presence of phlegm, coryza, and myalgia.
There was no statistically significant difference in the risk of confirmed seasonal influenza infection between recipients of TIV or placebo…
However, participants who received TIV had higher risk of ARI associated with confirmed noninfluenza respiratory virus infection.
Including 2 additional confirmed infections when participants did not report ARI, TIV recipients had higher risk of confirmed noninfluenza respiratory virus infection.
The majority of the noninfluenza respiratory virus detections were rhinoviruses and coxsackie/echoviruses, and the increased risk among TIV recipients was also statistically significant for these viruses. Most respiratory virus detections occurred in March 2009, shortly after a period of peak seasonal influenza activity in February 2009.
Receipt of TIV could increase influenza immunity at the expense of reduced immunity to noninfluenza respiratory viruses, by some unknown biological mechanism.*