Total revenues increased 11.3% and 11.2% for the three months and year ended December 31, 2022, respectively, compared to the prior year driven by growth across all product lines.
Adjusted operating income increased 68.2% for the three months ended December 31, 2022 compared to the prior year primarily driven by the net favorable impact of COVID-19 compared to the prior year and strong underlying performance, partially offset by the unfavorable impact of the flu compared to the prior year.
Adjusted operating income increased 19.4% for the year ended December 31, 2022 compared to the prior year primarily driven by the net favorable impact of COVID-19 compared to the prior year, strong underlying performance and membership growth. These increases were partially offset by incremental investments to support growth in the business, the unfavorable impact of the flu compared to the prior year and net realized capital losses.
The MBR decreased from 87.0% to 86.0% in the three months ended December 31, 2022 compared to the prior year and decreased from 85.0% to 84.0% in the year ended December 31, 2022 compared to the prior year. The decrease in both periods was primarily driven by the net favorable impact of COVID-19 compared to the prior year, partially offset by the unfavorable impact of the flu compared to the prior year.
Medical membership as of December 31, 2022 of 24.4 million increased 109,000 members compared with September 30, 2022, reflecting increases across all product lines.
Medical membership as of December 31, 2022 of 24.4 million increased 548,000 members compared with December 31, 2021, reflecting increases in Medicare and Commercial membership, as underlying Commercial growth more than offset the impact of international divestitures. These increases were partially offset by a decline in Medicaid membership reflecting the previously disclosed loss of a large customer in the third quarter of 2022.
The segment experienced favorable development of prior-periods’ health care cost estimates in its Government Services and Commercial businesses during the three months ended December 31, 2022, primarily attributable to third quarter 2022 performance.
Prior years’ health care costs payable estimates developed favorably by $654 million during the year ended December 31, 2022. This development is reported on a basis consistent with the prior years’ development reported in the health care costs payable table in the Company’s annual audited financial statements and does not directly correspond to an increase in 2022 operating results.