49.5% of the total number of shares of Armata’s common stock issued and outstanding as of the record date for voting on the matters related to election or removal of Armata’s board members. Currently, 3 of the 7 members of Armata’s board of directors are also members of the board of directors of Innoviva. As of June 30, 2021 and December 31, 2020, we owned approximately 59.5% and 46.6%, respectively, of Armata’s common stock.
The investment in Armata provides Innoviva and ISO the ability to have significant influence, but not control over Armata’s operations. Based on our evaluation, we determined that Armata is a VIE, but Innoviva and ISO are not the primary beneficiary of the VIE. We continue to elect the fair value option to account for both Armata’s common stock and warrants. The fair value of Armata’s common stock is measured based on its closing market price. The warrants purchased in 2020 and 2021 have an exercise price of $2.87 and $3.25 per share, respectively, are exercisable immediately within five years from the issuance date of the warrants and include a cashless exercise option. We use the Black-Scholes-Merton pricing model to estimate the fair value of these warrants with the following input assumptions: Armata’s closing market price on the valuation date, the risk-free interest rate computed based on the U.S. Treasury yield, the remaining contractual term as the expected term, and the expected stock price volatility calculated based on the historical volatility of the common stock of Armata and its peer companies.
As of June 30, 2021, the fair values of Armata’s common stock and warrants were estimated at $59.0 million and $41.9 million, respectively. As of December 31, 2020, the fair values of Armata’s common stock and warrants were estimated at $26.0 million and $18.0 million, respectively. The total fair value of both financial instruments in the amount of $100.9 million and $44.0 million was recorded as equity and long-term investments on the consolidated balance sheets as of June 30, 2021 and December 31, 2020, respectively. During the three and six months ended June 30, 2021, we recorded $24.3 million unrealized loss and $36.9 million unrealized gains, respectively, as changes in fair values of equity and long-term investments, net on the consolidated statements of income. We recorded $13.4 million and $35.3 million of unrealized gains for the three and six months ended June 30, 2020, respectively.
Equity Investment in Entasis
During the second quarter of 2020, we purchased 14,000,000 shares of common stock as well as warrants to purchase 14,000,000 additional shares of common stock of Entasis Therapeutics, Inc. (“Entasis”) for approximately $35.0 million in cash. Entasis is a clinical-stage biotechnology company focused on the discovery and development of novel antibacterial products.
During the third quarter of 2020, we purchased 4,672,897 shares of Entasis common stock as well as warrants to purchase 4,672,897 additional shares of its common stock for approximately $12.5 million in cash. Innoviva has a right to designate 2 members to Entasis’ board. As of June 30, 2021 and the date hereof, 0 Innoviva designees are serving on Entasis’ six-member board.
On May 3, 2021, ISO entered into a securities purchase agreement with Entasis to acquire 10,000,000 shares of Entasis common stock and warrants to purchase 10,000,000 additional shares of Entasis common stock for approximately $20.0 million. The investment was closed in 2 tranches on May 3, 2021 and June 11, 2021. This investment supports the continued development of Entasis’ novel pipeline of pathogen-targeted antibacterial product candidates. The additional investment increased Innoviva and ISO’s combined ownership, such that as of June 30,2021, we owned approximately 60.6% of Entasis’ common stock. As of December 31, 2020, we owned approximately 51.0% of Entasis’ common stock.
The investment in Entasis provides Innoviva the ability to have significant influence, but not control over Entasis’ operations. Based on our evaluation, we determined that Entasis is a VIE, but Innoviva is not the primary beneficiary of the VIE. We elected the fair value option to account for both Entasis’s common stock and warrants at fair value. The fair value of Entasis’ common stock is measured based on its closing market price at each balance sheet date. The warrants have an exercise price of $2.50 per share and $2.675 per share for those warrants acquired in the second and third quarter of 2020, respectively. The warrants acquired in the second quarter of 2021 have an exercise price of $2.00 per share. All of the warrants are exercisable immediately within five years from the issuance date of the warrants and include a cashless exercise option. We use the Black-Scholes-Merton pricing model to estimate the fair value of these warrants.
As of June 30, 2021, the fair values of Entasis’s common stock and warrants were estimated at $76.6 million and $54.7 million, respectively. As of December 31, 2020, the fair values of Entasis’s common stock and warrants were estimated at $46.1 million and $31.9 million, respectively. The total fair value of both financial instruments in the amount of $131.3 million and $78.0 million was recorded as equity and long-term investments on the consolidated balance sheets as of June 30, 2021 and December 31, 2020, respectively. We recorded $44.7 million and $33.2 million unrealized gains as changes in fair values of equity and long-term