Weekly new COVID-19 cases for California, New York, and Ohio, covering 20 January
2020 to 27 March 2023, built by taking first differences of the cumulative case
counts reported by The New York Times and summing them into Monday-starting ISO
weeks (matching wastewater_data). Negative day-to-day differences
(occasional downward revisions in the source data) were floored at zero before
summing. The New York Times repository stopped updating in March 2023, which sets
the end of this series. See data-raw/wastewater_data.R for the full
processing script.