The highly valued yet mysterious Moderna provided a peek at its first human data, reporting positive interim results from a phase 1 trial testing its mRNA-based H10N8 flu vaccine—a proof-of-technology project laying the groundwork for its entire pipeline.

Moderna picked that relatively safe target to reveal its first clinical data. CEO Stéphane Bancel told the Wall Street Journal that the company is only using the vaccine to test the mRNA waters rather than to commercialize the shot itself.

The study marks the first clinical data posted by Moderna, which operated in stealth mode until unveiling its clinical plan last January at the J.P. Morgan Healthcare Conference. It's been closely watched along the way because of its megafunding; to date the company has raised $1.9 billion for its efforts.

In this inaugural study, after 43 days, all 23 participants who received 100 µg of the company's vaccine achieved HAI titers indicating seroprotection against seasonal flu. None of the eight subjects in the placebo arm responded.

Three participants experienced adverse events that were labeled severe, including injection-site reactions and common cold-like symptoms, but investigators reported that the issues were "manageable and reversible." The vaccine was "safe and well tolerated" overall, according to the biotech.

Moderna expects to complete the 201-participant study at the end of this year, according to clinicaltrials.gov. It expects to report data in 2018.

The intermediate data were published online by Molecular Therapy, along with some strong preclinical data for Moderna’s second viral mRNA vaccine program, mRNA-1851, against H7N9 bird flu.

Phase 1 numbers, especially interim ones, don’t say much about a drug. But the team at Moderna appears satisfied and confident in the results and the promise they carry, since they do demonstrate to an extent that Moderna’s mRNA technology can work in vaccines.

Tal Zaks, M.D., Ph.D., chief medical officer, said in a statement that the data "provide important validation of our core mRNA platform, as we continue to advance our development pipeline, tackling more complex vaccines including personalized cancer vaccines, and moving our mRNA therapeutics into clinical development."

Based on the company’s more recent announcement at this year’s J.P. Morgan event in January, it now has 12 mRNA candidates under development in infectious diseases, immuno-oncology and cardiovascular disease. Eight are viral vaccines, including mRNA-1325, a Zika shot the company started phase 1 testing last December with NIAID help.

But more could be at stake with the company’s cancer vaccines, a field with high commercial potential that could contribute much more to Moderna's top line. The biotech has already inked deals with AstraZeneca and Merck & Co., and previously said that its vaccine "has the potential to be synergistic with checkpoint inhibitor therapies," including its partner Merck’s PD-1 therapy Keytruda.