Net income for the third quarter of 2021 included the after-tax impairment loss on internal-use software of $9.6 million or $0.05 per diluted common share, the after-tax amortization of the cost of reinsurance of $15.5 million or $0.08 per diluted common share, the net after-tax reserve decrease related to reserve assumption updates of $143.3 million or $0.70 per diluted common share, and a net after-tax realized investment loss on the Company's investment portfolio of $100,000 or a de minimis impact on earnings per diluted common share.
Net income in the third quarter of 2020 included after-tax costs related to an organizational design update of $18.6 million or $0.09 per diluted common share, and a net after-tax realized investment gain on the Company's investment portfolio of $3.8 million or $0.01 per diluted common share.
Excluding these items, after-tax adjusted operating income in the third quarter of 2021 was $210.5 million or $1.03 per diluted common share compared to $245.9 million or $1.21 per diluted common share in the year ago quarter.
On a year-over-year basis in the third quarter, Unum US generated an increase in premium income of 1.2%.
To put it in context, in the third quarter, the U.S. experienced a significant increase in national COVID mortality counts to approximately 94,000 lives, which is almost double the 52,000 in the second quarter.
In fact, just 90 days ago, most experts were estimating a third quarter mortality count of approximately 44,000 deaths, an estimate that has more than doubled over the course of the quarter.
Beyond the higher mortality counts in aggregate, data from the CDC also shows that the third quarter working-aged individuals comprised approximately 40% of the COVID-related mortality, double that of the fourth quarter of 2020 and first quarter of 2021 before vaccinations began to widely be available.
We start first with a capital position that remains very healthy with holding Company cash of $1.6 billion and weighted average risk-based capital ratio for our traditional U.S. -- U.S.-based life insurance companies at approximately 380%.
Last week, we were pleased to announce the $250 million share repurchase authorization approved by our Board, which we intend to initiate in the fourth quarter with an execution of an accelerated share repurchase of $50 million.
The biggest component of the actuarial reserve review was the release of $215 million before tax in the Unum US long-term disability line.
For the Closed Group Pension Block, policy reserves were increased by $25.1 million before tax.
For the Closed Disability Block, claim reserves were increased by $6.4 million before tax.
And finally for Long-Term Care, claim reserves were increased by $2.1 million before tax.
Although the net of these reserve updates are excluded from adjusted operating income, they did contribute $0.70 per share to the Company's book value.
For the third quarter in the Unum US segment, adjusted operating income was $88.5 million compared to $179.3 million in the second quarter.
Within the Unum US segment, the group disability line reported adjusted operating income, excluding the reserve assumption updates of $39.5 million in the third quarter compared to $59.9 million in the second quarter.
The primary driver of the decline was an increase in the benefit ratio to 78.9% in the third quarter compared to 74.7% in the second quarter, which was primarily driven by increased claims in the short-term disability line related to the COVID Delta variant and the current external environment.
Premium income declined slightly on a sequential quarter basis, but we were pleased to see an uptick in growth to 2.6% on a year-over-year basis.
Adjusted operating income for Unum US group life and AD&D declined to a loss of $67.1 million in the third quarter from income of $5.2 million in the second quarter.
This quarter-to-quarter decline of roughly $70 million was largely driven by the changing impacts from COVID that Rick described in his comments.
We were impacted by the deterioration in COVID-related mortality from our reported 52,000 national deaths in the second quarter to approximately 94,000 in the third quarter along with the age demographic shifting to higher impacts on younger working-aged individuals.
Estimated COVID-related excess mortality claims for our Group Life Block increased from approximately 800 claims in the second quarter to over 1,900 claims in the third quarter.
Accordingly, our results reflect mortality to level that represents approximately 2% of the reported national figures compared to a 1% rate experienced through 2020 when mortality was more pronounced in the elderly population.
With a higher percentage of working-age individuals being impacted, we also experienced higher average benefit size, which increased from around $55,000 in the second quarter to over $60,000 this quarter.
Looking ahead to the fourth quarter, our current expectation is for U.S. COVID-related mortality to continue to worsen to approximately 100,000 deaths.
Now looking at the Unum US supplemental and voluntary lines, adjusted operating income totaled $116.1 million in the third quarter compared to $114.2 million in the second quarter, both very good quarters that generated adjusted operating returns on equity in excess of 17%.
The uptick in the benefit ratio in the third quarter to 46.6% from 44.2% in the second quarter was driven by increased COVID-related life insurance claims, which offset generally favorable results in the other VB product lines.
Finally, utilization in the dental and vision line improved, leading to an improvement in the benefit ratio to 75% this quarter from 77.1% in the second quarter.
Looking now at premium trends and drivers, total new sales for Unum US increased 7.7% in the third quarter on a year-over-year basis compared to the declines that we experienced in the first half of the year.
For the employee benefit lines which do include LTD, STD, group life, AD&D and stop-loss, total sales declined by 2.5% this quarter, primarily driven by lower sales in a large case market and generally flat sales in the core market, which are those -- which are those markets under 2,000 [Phonetic] lines.
Sales trends in our supplemental and voluntary lines rebounded strongly in the quarter, increasing 21.8% in total when compared to the year ago quarter.
We saw sharp year-over-year increases in the recently issued individual disability line up 22.9% and in the dental and vision line up 48.2%.
Voluntary benefit sales also recovered following lower year-over-year comparisons in recent quarters, growing 13.7% in the third quarter.
Our group lines aggregated together showed a slight uptick to 89.4% for the first three quarters of 2021 compared to 89.1% last year.
We had very good -- we had a very good quarter with adjusted operating income for the third quarter of $27.4 million compared to $24.8 million in the second quarter, a continuation of the improving trend in income over the past several quarters.
The primary driver of these results is our Unum UK business, which generated adjusted operating income of GBP18.4 million in the third quarter compared to GBP16.8 million in the second quarter.
The reported benefit ratio for Unum UK improved to 79.2% in the third quarter from 82.5% in the second quarter.
Looking at the growth on a year-over-year basis and in local currency to neutralize the benefit we saw from the higher exchange rate, Unum UK generated growth of 2.9% with strong persistency and the continued successful placement of rate increases on our in-force block.
Additionally, sales in Unum UK rebounded in the third quarter, increasing 40.2% over last year.
Unum Poland also generated growth of 12.5%, a continuation of the low double-digit premium growth this business has been producing.
Next, results for Colonial Life are in line with our expectations for the third quarter with adjusted operating income of $80.1 million compared to the record quarterly income of $95.8 million in the second quarter.
As with our other U.S.-based life insurance businesses, Colonial's life insurance block was negatively impacted by COVID-related mortality, which was the primary driver in pushing the benefit ratio to 55.9% in the third quarter compared to 51.7% in the second quarter.
We estimate that adverse COVID-related claims experienced in the life block impacted results by approximately $16 million, the worst impact we have seen from COVID throughout the pandemic and a level that is likely to persist through the fourth quarter.
Additionally, net investment income increased 25% on a sequential basis in the third quarter, largely reflecting unusually large bond call activity this quarter.
We do not expect the benefit from bond calls to net investment income to continue at this level in the fourth quarter.
Driving this improving trend in premiums is a continuing rebound in sales activity at Colonial Life increasing 28.6% on a year-over-year basis this quarter and now showing a 21.1% increase for the first three quarters of 2021 relative to last year.
Persistency for Colonial Life continues to show an encouraging trend at 78.9% for the first three quarters of 2021, more than a point higher than a year ago.
In the Closed Block segment, adjusted operating income which does include -- which excludes the reserve assumption updates and the amortization of cost of reinsurance related to the Closed Block individual disability reinsurance transaction that did fully close earlier this year was $109.8 million in the third quarter and $111.2 million in the second quarter, both very strong results driven by favorable overall benefits experience in both the Long-Term Care line and Closed Disability Block, and strong levels of investment income to -- due to higher than expected levels of miscellaneous investment income, which I will cover in more detail in a moment.
The interest adjusted loss ratio in the third quarter was 74.8% and over the past four quarters is 71.8%, which are both well below our longer-term expectation of 85% to 90%.
In the third quarter, we continue to see higher mortality experience in the claimant block, where accounts were approximately 5% higher than expected which is similar to our experience in the second quarter.
For the Closed Disability Block, the interest adjusted loss ratio was 58.2% in the third quarter compared to 69.6% in the second quarter, both very favorable results for this line.
Looking ahead, we estimate the quarterly adjusted operating income for this segment will over time run within a range of $45 million to $55 million, assuming more normal trends for investment income and claim results in the LTC and Closed Disability lines.
We recorded approximately $20 million in higher investment income from bond calls this quarter relative to our historic -- our historical quarterly averages.
Second, we continue to see strong performance in our alternative investment portfolio, which earned $38.2 million in the third quarter, following earnings of $51.9 million recorded in the second quarter.
Both quarters are well above the expected quarterly income on the portfolio of $12 million to $14 million.
The weighted average risk-based capital ratio for our traditional U.S. insurance companies improved to approximately 380%, and holding company cash was $1.6 billion as of the end of the third quarter, both of which are well above our targeted levels.
In addition, leverage has trended lower with equity growth and is now 25.7%.
We began to roll our plans out last week with the announcement of the authorization by our Board of Directors and to repurchase up to $250 million of our shares by the end of 2022.
We plan to begin this program with the execution of an accelerated share repurchase of $50 million in the fourth quarter.
With this additional deployment of capital, we continue to project having a very solid capital position at the end of 2022 with holding company cash around $1 billion and an RBC ratio well above our target.
Now shifting topics, I wanted to give you a brief update on our progress in adopting ASC 944 or Long Duration Targeted Improvements.
With COVID-related mortality expected to increase further in the fourth quarter to approximately 100,000 nationwide deaths, we expect to see similar, if not slightly worse trends for mortality impacts on our life insurance businesses in the fourth quarter than we did experience in the third quarter.

Summary:
Excluding these items, after-tax adjusted operating income in the third quarter of 2021 was $210.5 million or $1.03 per diluted common share compared to $245.9 million or $1.21 per diluted common share in the year ago quarter.
We do not expect the benefit from bond calls to net investment income to continue at this level in the fourth quarter.