These results serve as the foundation for our exceptional net income result of over $1 billion through the first half of 2021, and another important step to achieving our three-year strategic plan objectives and the delivery of superior results to our shareholders.
Everest achieved an annualized total shareholder return of 22.5% through the first half of 2021, while exceeding our three-year strategic planned target of 13%.
We grew gross written premiums by 35% and net written premiums by 39%.
The combined ratio was 89.3%, an 8-point improvement year-over-year.
The attritional combined ratio was 87.6%, almost a four point better than prior year, with both segments expanding margins.
We generated $274 million in underwriting profit compared to $51 million in the second quarter last year.
Net investment income was simply outstanding at $407 million, compared to $38 million in the prior year second quarter.
These strong operating results led to a net income for the quarter of $680 million, resulting in an annualized return on equity of over 28%.
Gross written premiums in reinsurance were up 40% over the second quarter of 2020.
The attritional combined ratio, ex COVID-19 pandemic impact was 86.1% for the quarter, a 60 basis point improvement year-over-year, resulting from our continued focus on loss and expense management.
We wrote over $1 billion in gross written premiums for the first time in a quarter.
This represents 25% growth year-over-year or 30% growth, excluding workers' compensation.
We also delivered strong underwriting results with a 93.5% combined ratio, a 10-point improvement over the same period last year, which was impacted by COVID.
The underlying performance was also excellent with a 92.1% attritional combined ratio, a 1.6% improvement over last year and almost four points better than the second quarter of 2019.
Renewal rate increases continued to exceed our expectations for loss trend, up 14% in the quarter, excluding workers' compensation, and up 11%, including workers' compensation.
Rate increases were led by excess casualty, up 22%; property, up 16%; financial lines, up 14% and general liability, up 9%.
We continue to thoughtfully manage the workers' compensation line, which now represents 10% of our second quarter premiums, down from 14% year-over-year.
For the second quarter of 2021, Everest reported gross written premium of $3.2 billion, representing 35% growth over the same quarter a year ago.
By segment, reinsurance grew 40% to $2.1 billion and insurance reported its first-ever $1 billion top line quarter, representing 25% growth year-over-year.
For the second quarter, Everest reported net income of $680 million, resulting in an annualized return on equity of 28%.
We also reported net operating income of $587 million, equal to operating earnings of $14.63 per share and an annualized operating return on equity of 24.5%.
All three of our earnings engines provided meaningful contributions with significant underwriting income from both our reinsurance and insurance franchises, capped off by net investment income of $407 million, a record quarterly net investment income result.
The underwriting income during the quarter of $274 million reflects Everest's disciplined execution of our strategy to grow and expand margins.
The combined ratio was 89.3% for the quarter, compared to 97.5% last year.
Catastrophe losses during the quarter of $45 million are pre-tax and net of reinsurance and reinstatement premiums, with $35 million in the reinsurance segment and $10 million in the insurance segment, representing additional IBNR provisions for Winter Storm Uri.
Finally, I note we have not added to our COVID-19 incurred loss provision, which remains at $511 million, with the vast majority remaining as IBNR.
Excluding the catastrophe losses, reinstatement premiums, prior year development and COVID-19 pandemic impact, the attritional loss ratio for the group was 60.3% in the second quarter of 2021, compared to 60% in the second quarter of 2020.
The year-to-date attritional loss ratio for the group was 60.5% compared with 60.7% a year ago.
The attritional combined ratio for the group was 87.6% for the second quarter compared to 88.5% for the second quarter of 2020, representing a 0.9 point improvement.
Year-to-date, attritional combined ratio for the group was 87.4% compared with 89.1% a year ago, representing a 1.7 point improvement.
For insurance, the attritional loss ratio improved to 64.2% in the second quarter of 2021 compared with 65.1% year-over-year.
The attritional combined ratio for insurance improved to 92.1% as compared to 93.7% over the same period of time.
For reinsurance, the second quarter 2021 attritional loss ratio was 59.1% compared with 58.2% a year ago.
The attritional combined ratio was 86.1% for the second quarter, down from 86.7% for the second quarter of 2020.
The group commission ratio of 21.8% for the second quarter of 2021 was down 100 basis points from 22.8% reported in Q2 2020, largely due to changes in the composition of our business mix.
The expense ratio remained low at 5.5% for the quarter as compared with 5.8% reported a year ago, and the expense ratio continues to benefit with our continued focus on expense management and the increased scale and efficiency of our operating model.
For the second quarter, investment income had an exceptional result of $407 million as compared to $38 million for Q2 2020.
Alternative investments accounted for $266 million of income during the second quarter, largely due to increases in the reported net asset values of our diversified limited partnership investments.
Invested assets at the end of the second quarter totaled $27.1 billion compared to $21.6 billion at the end of Q2 2020 and $25.5 billion at year-end 2020.
Approximately 80% of our invested assets are comprised of a well-diversified high credit quality bond portfolio with a duration of 3.6 years.
Our effective tax rate on operating income for the second quarter of 2021 was 9.3% and 10.6% on net income.
This was a favorable variance versus our estimated tax rate of approximately 11% based on the geographic distribution of income.
For the first six months of 2021, Everest generated a record $1.6 billion of operating cash flow, compared to $1.1 billion for the first half of 2020, reflecting the strength of our premium growth year-over-year.
Shareholders' equity was $10.4 billion at the end of the second quarter 2021, compared with $9.7 billion at year-end 2020.
We repurchased $16.8 million of shares in the quarter.
Our debt leverage ratio is 13.3% or approximately 15.5% inclusive of our $310 million short-term loans from the Federal Home Loan Bank.
Book value per share was $260.32 at the end of the second quarter compared with $241.57 at the end of Q1 2021, reflecting dividend adjusted growth of 8.4%.
And for the year-to-date, the TSR number is 22.5% annualized.

Summary:
We grew gross written premiums by 35% and net written premiums by 39%.
We also reported net operating income of $587 million, equal to operating earnings of $14.63 per share and an annualized operating return on equity of 24.5%.