Last December, we announced a milestone of 100,000 DaVita patients who have received transplant since the year 2000.
New COVID infections among our patients continue to drop significantly through the last week of June down more than 90% from the peak in early January.
As of last week on a rolling seven day average basis new infection, they're still down more than 90% from the peak.
As a result, we delivered 6% year-over-year growth in adjusted operating income and 35% year-over-year growth in our adjusted earnings per share.
We are preparing to partner with nephrologists and up to 12 markets beginning in January of next year to participate in CKCC voluntary program.
With our special needs plan we have been able to lower mortality by 23% relative to other patients within the same-center and county.
As of today, approximately 10% of our US dialysis patients are in value-based care arrangements in which Tervita is responsible for managing the total cost of care.
This represents almost $2 billion of annual medical cost under management.
We expect to incur a net operating loss of $120 million in 2021 in our US ancillary segment this outcome is consistent with the OII headwinds from ITC growth, we called out at the beginning of the year and is of course included in our full year guidance.
The doubling of the business next year could result and an incremental operating loss in our ancillary segment of $50 million in 2022.
Currently we serve approximately 200,000 dialysis patients across the country, we utilize over $12 billion in health services outside of the dialysis facility, including the cost of hospitalization, our patient procedures and physician services.
For the quarter, operating income was $490 million and earnings per share were $2.64.
Our Q2 results include a net COVID headwind of approximately $35 million similar to what we saw in Q1.
In Q2 treatments per day increased by 0.4% compared to Q1.
Excess mortality declined significantly in Q2 from approximately 3,000 in Q1 to fewer than 500 in Q2.
Our US dialysis revenue per treatment grew sequentially by almost $6 this quarter, primarily due to normal seasonal improvements from patients meeting their co-insurance and deductible obligations.
During the second quarter, we generated a gain of approximately $9 million on one of our DaVita Venture Group investments which hit the other income line on our P&L.
The value of this investment at quarter end was $23 million going forward market-to-market every quarter.
Adjusted earnings per share of $8.80 to $9.40.
Adjusted operating income of $1.8 billion to $1.875 billion and free cash flow of $1 billion to $1.2 billion.
Also we now expect our 2021 effective tax rate on income attributable to DaVita to be between 24% and 26% lower than the 26% to 28% range that we had communicated at the beginning of the year.
I'll call out two notable potential headwind during the second half of the year.
As a result, we are increasing the middle of the range of COVID impact for the full year to $170 million from $150 million.
That implies a $30 million headwind from COVID in the second half of the year compared to the first half of the year.
Second, we expect to experience losses in our US ancillary segment of approximately $70 million in the second half of the year compared to $50 million in the first half of the year.

Summary:
For the quarter, operating income was $490 million and earnings per share were $2.64.
Adjusted earnings per share of $8.80 to $9.40.
I'll call out two notable potential headwind during the second half of the year.