Turning to Slides 3 and 4.
My comments are summarized across Slide 6 and 7 in the deck accompanying the call.
This option exercise is valued at approximately $182 million and requires all doses to be delivered by the end of this calendar year.
This quarter, we also secured the next option exercise for our smallpox therapeutic VIGIV product valued at approximately $56 million.
COVID-HIG leverages our polyclonal hyperimmune platform and continues to show neutralizing activity against variants of SARS-CoV-2 virus in, in vitro models.
We anticipate in the near-term, the initiation of a Phase 3 study led by NIAID assessing the effect of hyperimmunes on patient populations that have not yet progressed to severe disease to determine the progression can be impacted.
In addition, as we have previously discussed, the U.S. circuit court of appeals has scheduled the oral argument for NARCAN U.S. appeal for August 2 on the ongoing Patent Infringement Litigation.
We still expect to initiate a Phase 3 trial for Chikungunya virus VLP vaccine in 2021.
In addition, and then supported this important development program, we recently announced positive two-year persistence data from a Phase 2 clinical study that indicated that our vaccine candidate appears to generate a rapid and durable immune response.
We also plan to initiate a Phase 1 study in late 2021 and early 2022, related to a number of vaccine candidates in the pipeline, including our Shigella, Lassa and universal flu vaccine candidates.
As you can see, we expect that the remainder of 2021 will be busy for our product development teams, including clinical regulatory and quality as our pipeline continues to mature.
On the personnel front, we recently issued an 8-K announcing the reorganization of my direct reports, Rich Lindahl, our Chief Financial Officer; Karen Smith, our Chief Medical Officer and Katy Strei, our Chief Human Resources Officer continued to report directly to me.
We have a deep appreciation for Sean's 18 years of service at Emergent and wish him the very best for him and his family going forward.
A quick run through of key highlights include, total revenues of $398 million, an increase of $3 million versus the prior year and in line with our guidance and adjusted EBITDA $50 million and adjusted net income of $18 million both decreases versus the prior year due to a variety of one time and other expenses, which we will discuss in a moment.
Breaking down quarterly revenue into its components, anthrax vaccine sales were $52 million lower than the prior year due to timing of deliveries.
NARCAN nasal spray sales were $106 million, an increase over the prior year, driven by continued strong demand for this critical drug device combination product for opioid overdose reversal across both the retail and public interest channels in the U.S., as well as increased Canadian sales.
Other products sales were $24 million consistent with the prior year and CDMO services revenue came in at $191 million, an increase over the prior year and reflecting contributions from all three service pillars, primarily for our government and innovator partners response to the COVID-19 pandemic.
As Bob noted in his remarks, earlier in July, the U.S. government exercised the next ACAM2000 contract option that is valued at $182 million.
Looking beyond revenue, the quarterly results also include cost of goods sold of $228 million, a $98 million increase over the prior year.
And reflecting the increased costs associated with a substantial increase in CDMO services revenues, as well as $42 million of inventory write-offs, which I will return to in a moment.
Gross R&D expense of $49 million consistent with the prior year, reflecting our continued commitment to investing in our pipeline of development programs across our three product focused business units.
Net R&D expense of $24 million or 6% of adjusted revenue consistent with the prior year, SG&A spend of $91 million or 23% of total revenues, an increase over the primary prior year, and primarily reflecting the impact of higher costs to support and defend our corporate reputation and combined product and CDMO gross margin of $144 million or 39% of adjusted revenue, a decline of $97 million and reflecting the impact of $42 million of inventory write-offs due to raw materials and in-process batches at the Bayview facility that the company plans to discard as they were deemed unusable.
$43 million associated with the product and service revenue mix, which was weighted more heavily to lower margin products and services and $12 million associated with costs incurred to remediate and strengthen manufacturing processes at our Bayview facility, many of which are temporary in nature.
In the second quarter, we continue to obtain incremental contract awards resulting in secured new business of $53 million.
However, this outcome was significantly offset by $108 million of negative contract modifications.
As of June 30, the backlog is $1.1 billion.
And lastly, as of June 30, the opportunity funnel was $672 million down from $807 million at March 31.
Moving onto Slide 13 for a review of our balance sheet and cash flow, we ended the second quarter in a strong liquidity position with $448 million in cash and $262 million of accounts receivable resulting in aggregate current liquid assets of nearly $710 million.
This compares with approximately $732 million of aggregate current liquid assets as of the end of the first quarter.
We also still have undrawn revolver capacity of just under $600 million.
Finally, at the end of the second quarter, our net debt position was $416 million.
And our ratio of net debt to trailing 12 month adjusted EBITDA remained below one times.
One consideration that has been revised is that our expectation for gross margin for the full year is now approximately 61% to 63% on a GAAP basis, a reduction of 200 basis points from the prior range of 63% to 65%.
This change reflects the impact of the Q2 2021 performance as well as expectations for the remainder of the year.
Lastly, we are providing third quarter total revenue guidance of $400 million to $500 million.
On a year-to-date basis, our revenues of $741 million represent approximately 41% of our full year 2021 forecasted total revenues at the midpoint, a similar waiting between first half and second half total revenues as has occurred in each of the last four years.

Summary:
As you can see, we expect that the remainder of 2021 will be busy for our product development teams, including clinical regulatory and quality as our pipeline continues to mature.
On the personnel front, we recently issued an 8-K announcing the reorganization of my direct reports, Rich Lindahl, our Chief Financial Officer; Karen Smith, our Chief Medical Officer and Katy Strei, our Chief Human Resources Officer continued to report directly to me.
This change reflects the impact of the Q2 2021 performance as well as expectations for the remainder of the year.
Lastly, we are providing third quarter total revenue guidance of $400 million to $500 million.