Post-COVID rebound in invasive pneumococcal disease driven by resurgence of serotype 4 among American Indian individuals in the Southwest United States.

Abstract

Incidence of invasive pneumococcal disease (IPD) in American Indian (AI) communities in the Southwest US declined during the COVID-19 pandemic. We estimated the burden and serotype distribution of IPD in the same communities in 2022-24. We conducted active, laboratory-based surveillance for IPD in the Navajo Nation and White Mountain Apache Tribal (WMAT) lands. Isolates were collected and serotyped. Annual incidence rates were calculated and serotype distribution was estimated. The proportion of serotypes covered by available pneumococcal conjugate vaccines (PCV20 and PCV21) were estimated and compared by age group using McNemar's Chi-squared or Exact McNemar tests, as appropriate. IPD rates increased from 2022 to 2024 to pre-pandemic levels; from 45.9 to 62.1 per 100,000 in the Navajo Nation and 52.9 to 84.4 in the WMAT lands. Among adults in the Navajo Nation, serotype 4 accounted for 28.5% of cases and occurred primarily among younger unvaccinated males. The proportion of cases covered by PCV21 was lower than PCV20 for adults 18-49 years (53.2% vs 77.3%; p<0.001) but higher for adults ≥65 years (82.5% vs 65.1%; p=0.03). In the WMAT lands, no cases of serotype 4 were identified; the proportion of cases covered by PCV21 was the same or higher than for PCV20 across age groups. In two AI communities in the Southwest, IPD rates returned to pre-pandemic levels. In the Navajo Nation, the increase was driven by serotype 4 IPD among younger male unvaccinated adults. These findings can inform vaccine recommendations and highlight the value of surveillance.