Influence of respiratory viruses on the evaluation of the 13-valent pneumococcal conjugate vaccine effectiveness in children under 5 years old: A time-series study for the 2001-2013 period.

INTRODUCTION: S treptococcus pneumoniae is the main agent in bacterial consolidated pneumonias. In 2012, the 13-valent pneumococcal conjugate vaccine was introduced in the Argentine national immunization schedule for immunocompetent children as of two months old with a two-dose schedule plus a booster.

OBJECTIVE: To analyze the influence of respiratory viruses on the evaluation of the 13-valent pneumococcal conjugate vaccine effectiveness in relation to the number of hospitalizations for radiologically-confirmed consolidated pneumonias (RCCP).

METHODS: Observational, analytical, time-series study. All children hospitalized with a diagnosis of RCCP as per the World Health Organization's criteria between March and November throughout the2001-2013period were included. Viral diagnosis (respiratory syncytial virus, adenovirus, influenza and parainfluenza) was performed by indirect immunofluorescence using nasopharyngeal aspirates or by reverse transcription polymerase chain reaction. Time-series were developed to compare preimmunization 2001-2011 and post-immunization 2012-2013 periods.

RESULTS: Out of a total of 11,306 children under 5 years old with acute lower respiratory tract infections, 4974 with RCCP were included. Annual average number of hospitalizations for RCCP: 394.8 pre-immunization, 315.5 post-immunization (reduction of 20.1%, 95% confidence interval |-CI-|: 13.13-26.49%, p < 0.001). Annual average number of hospitalizations for non-viral RCCP: 255.5 pre-immunization, 183 post-immunization (reduction of 28.4%, 95% CI: 20.5-35.78%, p < 0.001). Annual average number of hospitalizations for viral RCCP: 139.2 pre-immunization, 132 post-immunization (reduction of 4.8%, 95% CI: 8.38-16.49%, p= 0.4758). The proportion of RCCP with positive viral diagnosis was 35.3 % pre-immunization and 42% post-immunization (p= 0.001).

CONCLUSIONS: An overall significant reduction in the number of hospitalizations for RCCP was observed following the introduction of the 13-valent pneumococcal conjugate vaccine, especially in the case of non-viral pneumonias. It is critical to continue with the epidemiological surveillance to evaluate the impact of this intervention and viral behavior in relation to RCCP.