Despite pushback from intellectual property activists at Knowledge Ecology International (KEI) and high-profile politicians, a U.S. Army official dismissed concerns about a pending license transfer for a Zika vaccine candidate to pharma giant Sanofi.

Responding to criticism of the proposed deal, the U.S. Army’s director of medical technology transfer at the Medical Research and Materiel Command, Barry Datlof, wrote (PDF) last week that the deal will comply with U.S. laws and will "be in the best interest of the U.S. government and the public." KEI released the letter Monday.

Originally developed by Army scientists, the immunization went into phase 1 testing with National Institutes of Health support. Sanofi joined the effort to prepare for phase 2 trials and to create a clinical development and regulatory strategy.

KEI, a Washington, D.C.-based nonprofit, started protesting the proposed license soon after the U.S. government disclosed the plan in December. Highlighting the extensive government funding for the program—$43 million so far, with the potential for more—KEI asked for pricing safeguards and argued that the license transfer would "not be legal" because it isn’t necessary to motivate Sanofi to develop the vaccine.

In his response to KEI director Jamie Love, Datlof said it’s not feasible for the Army to "define, implement and enforce 'affordable prices' or to set price controls for a potential vaccine that will require great investment and face high risk of failure."

The agreement hasn’t been finalized, Datlof wrote, but the Army still plans to issue the license.

"Considering the high risk and high cost involved in advanced vaccine development, granting an exclusive license for a federally developed technology is often the only incentive significant enough to attract a competent and willing commercial partner," Datlof explained in the letter.

Love commented on KEI's website that his group will appeal. "The notion that this is too hard a task is not compelling," he said, adding that a pricing assurance in the license would be "very simple."

Since KEI started criticizing the deal, international charity Médecins Sans Frontières and politicians in the U.S. have joined in to register their opposition. Last month, frequent pharma critic Sen. Bernie Sanders called on the Trump Administration to call off a "bad deal" in a New York Times op-ed.

Sanofi has also taken a chance to voice its position on the license. In a separate NYT op-ed, R&D chief Elias Zerhouni, who saw plenty of public-private collaboration during his time as National Institutes of Health director, said vaccine development "entails tremendous costs and risks." If the vaccine did reach the market, Sanofi would owe "significant" milestone and royalty payments to the government, Zerhouni pointed out.

Testing a variety of approaches to Zika immunization, other branches of the federal government are in separate collaborations with Big Pharma players GlaxoSmithKline and Takeda.