Background: Infections occurring among vaccinated persons (vaccine failures) are known to occur in vaccines with imperfect efficacy. Failures among vaccinated children who were infected with vaccine-matched influenza B virus strain have not been adequately characterized.
Methods: Taking advantage of a randomized controlled trial of trivalent seasonal influenza vaccine (TIV), the viral shedding and clinical symptoms associated with reverse transcriptase polymerase chain reaction-confirmed influenza B infection and serum hemaggluttination inhibiting antibody response to vaccine were compared between children 6 and 17 years receiving TIV and placebo.
Results: Vaccine failures were observed to show lower antibody response to TIV compared with other vaccine recipients. We did not find any evidence that vaccination reduced the severity or duration of clinical symptoms of reverse transcriptase polymerase chain reaction-confirmed vaccine-matched influenza B infections. Vaccination was not observed to alter viral load or shedding duration.
Conclusions: TIV was not observed to ameliorate clinical symptoms or viral shedding among vaccine failures compared with infected placebo recipients. Lower antibody response might have explained vaccine failure and also lack of effect in reducing clinical symptoms and viral shedding upon infection. Our results are based on a randomized controlled trial of split virus inactivated vaccine and may not be applicable to other vaccine types. Further studies in vaccine failure among children will be important in future vaccine development.