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 (relative risk: 4.40; 95% confidence interval: 1.31-14.8). Being protected against influenza, TIV recipients may lack temporary non-specific immunity that protected against other respiratory viruses.
Cowling BJ, Fang VJ, Nishiura H, Chan KH, Ng S, Ip DK, Chiu SS, Leung GM, Peiris JS. (2012). Increased risk of noninfluenza respiratory virus infections associated with receipt of inactivated influenza vaccine. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 54(12)