Infant hospitalizations for pertussis before and after Tdap recommendations for adolescents

Recent universal vaccination efforts among children in the United States have markedly changed hospitalization patterns for many vaccine-preventable diseases. Infants with pertussis often require hospitalization to monitor for potentially life-threatening respiratory failure. In 2006, tetanus-diphtheria-acellular pertussis (Tdap) vaccination was recommended for universal administration to adolescents, a known source of pertussis in infants. By 2011, 78% of adolescents in the United States had received Tdap. We sought to understand if patterns of pertussis hospitalization for infants changed with adoption of Tdap vaccination among adolescents.

Infants (aged <1 year) diagnosed with pertussis were identified in the Nationwide Inpatient Sample by using diagnostic codes. We used variance-weighted least-squares regression over preimplementation years (2000-2005) to estimate pertussis hospitalization patterns if Tdap had not been available. We compared expected hospitalization rates with observed rates for 2008-2011. Two years (2006 and 2007) were excluded from analysis during early Tdap implementation.

The incidence of hospitalization for pertussis in 2000 was 5.82 (95% confidence interval: 4.51-7.13) discharges per 10,000 infants in the US population. The rate increased during pre-Tdap years by a mean of 0.64 pertussis discharges per 10,000 infants per year (P for trend = .004). Observed hospitalization rates for pertussis among infants were significantly lower than expected in 2008, 2009, and 2011, but in 2010 the observed and expected rates of hospitalization were not significantly different.

Adolescent Tdap vaccination appears to be partially effective in preventing pertussis hospitalizations among infants. However, broader Tdap immunization coverage may be necessary to achieve sustainable reductions in infant pertussis burden.