Differential Impact of Pneumococcal Conjugate Vaccines on Hospitalized Versus Outpatient Community-Acquired Alveolar Pneumonia in Children Younger Than 5 Years Suggests Differences in Pathogenesis.

BACKGROUND

Current evidence suggests that in young children with community-acquired alveolar pneumonia (CAAP), bacterial-viral coinfections (mostly respiratory syncytial virus [RSV]-pneumococcus coinfections) are more prevalent among hospitalized children than among outpatients and that RSV-pneumococcal coinfections are more frequently associated with non-PCV13 serotypes. Based on this background, we speculated that following pneumococcal conjugate vaccine [PCV] implementation, the decline of hospitalized CAAP episodes would be lower than that of outpatient episodes.

METHODS

This analysis was a part of an ongoing (since 2004) population-based, active surveillance in children < 5 years, including all CAAP visits to the pediatric emergency room in southern Israel. Community-acquired alveolar pneumonia was radiologically confirmed by consensus reading. Episodes were divided into hospitalized and those discharged without hospitalization (outpatients). We used a negative binomial regression model to evaluate PCV7/PCV13 impact by age and ethnic group using monthly and yearly incidence rates. Analyzed periods were pre-PCV (2004-2009), PCV7/PCV13 transition (2009-2011), early-PCV13 (2011-2015), and late-PCV13 (2015-2019).

RESULTS

Of 11 130 episodes, 3677 and 7633 were outpatients and hospitalized, respectively. Post-PCV incidence dynamics significantly diverged between the 2 study groups. (1) During the PCV7/PCV13 transition, outpatient rates significantly declined, but not those of hospitalizations. 2) During late-PCV13 period, a significantly greater decline was reached among outpatients (67%; 95% confidence interval [CI] 62%-71%) versus hospitalized (47%; 95% CI 41%-54%). This difference remained for all age and ethnic groups.

CONCLUSIONS

The marked divergence in PCV impact between hospitalized and outpatient episodes is intriguing, but consistent with previous studies suggesting that hospitalized CAAP was associated with a lower proportion of PCV13 serotypes, in conjunction with viral-bacterial (mostly RSV-pneumococcus) coinfections.