Background: Recent declines in childhood vaccination coverage in the United States are likely to continue or accelerate. Vaccine hesitancy is increasing while federal guidelines are changing to remove universal recommendations for several childhood vaccines. To provide state-specific projections of health and economic impacts, we developed an interactive tool to estimate the additional burden from declining infant vaccination.

Methods: We used calibrated, state-level equilibrium transmission models for rotavirus, pertussis, and invasive pneumococcal disease (IPD). Rotavirus was modeled using a Susceptible-Infection-Recovered model; pertussis and IPD used a Susceptible-Infection-Recovered-Susceptible model with waning immunity. Vaccine coverage declines of 0-20 percentage points were applied to infant cohorts. We calculated the impacts after one and five years of reductions accumulated across birth cohorts. Outcomes included additional annual cases, hospitalizations, deaths, and total costs.

Results: After a 20% decline in coverage over one year, we estimated annual impacts of 230,358 additional rotavirus cases (3,294 hospitalizations), 13,559 pertussis cases (644 hospitalizations), and 1,426 IPD cases (1,183 hospitalizations), with additional costs of $259M, $44M, and $25M, respectively. When coverage declined by 20% for five years, the annual impacts were 809,819 rotavirus cases (11,580 hospitalizations), 56,502 pertussis cases (2,768 hospitalizations), and 4,631 IPD cases (3,844 hospitalizations), with costs exceeding $911M, $183M, and $81M, respectively.

Conclusions: Sustained vaccination declines are projected to generate substantial and escalating health and economic losses. VaxImpact provides an interactive, state-specific platform enabling policymakers and public health practitioners to quantify projected disease and economic burden under varying decline scenarios, supporting immunization policy decisions and outbreak prevention efforts.