Using observations from nationwide seroprevalence studies, we have described proportions seropositive as a function of age and time during the SARS-CoV-2 pandemic in the United States. Slices through this surface at arbitrary times provide initial and target conditions for simulation modeling. They also provide the wherewithal for calculating age-specific forces of infection, attack rates, and – together with contact rates and a mixing matrix from the literature – probabilities of infection on contact between susceptible and infectious people. Values for most other transmission model parameters can be found by carefully reviewing the literature or consulting subject-matter experts. The estimated parameters are used in a metapopulation model for COVID-19 to identify vaccination strategies.