Shares of Cambridge, Mass.-based Moderna Inc. (NASDAQ:MRNA) were trading midday at $84.27, up $17.58, or 26%, on word of encouraging interim data with COVID-19 vaccine mRNA-1273 from the phase I study led by the NIH.

Data for the 25-µg and 100-µg dose level (in patients ages 18 to 55) after two doses (day 43) and at the 250-µg level (in patients ages 18 to 55) after one dose (day 29) show dose-dependent drops in immunogenicity across all three levels, as well as between prime and boost within the 25-µg and 100-µg dose levels. All participants ages 18 to 55 (n=15 per cohort) across levels seroconverted by day 15 after a single dose.

At day 43, two weeks following the second dose, at the 25-µg dose level (n=15), levels of binding antibodies were at the levels seen in convalescent sera (i.e., blood samples from people who have recovered from COVID-19) tested in the same assay. At the 100-µg dose level (n=10), levels of binding antibodies significantly exceeded the levels seen in convalescent sera. Samples are not yet available for remaining participants, Moderna said.

Neutralizing-antibody findings are available only for the first four participants in each of the 25-µg and 100-µg dose level cohorts. Consistent with the binding antibody data, mRNA-1273 vaccination elicited neutralizing antibodies in all eight of those participants, as measured by plaque reduction neutralization assays against live SARS-CoV-2. The levels of neutralizing antibodies at day 43 reached or surpassed levels typically seen in convalescent sera.

The vaccine was generally safe and well-tolerated, with a safety profile consistent with that seen in previous Moderna infectious disease vaccine clinical studies. The sole incidence of a grade 3 adverse event (AE) in the 25-µg and 100-µg dose cohorts involved a participant at 100 µg who experienced redness around the injection site. So far, the most notable AEs turned up at the 250-µg dose level, where three subjects exhibited grade 3 systemic symptoms, only following the second dose. All AEs have been transient and self-resolving, Moderna noted. Researchers chalked no grade 4 events or serious AEs.

Preclinical results from a viral challenge study in mice are also available. Vaccination with mRNA-1273 prevented replication in the lungs of animals challenged with the virus. Neutralizing titers in phase I participants at the 25-µg and 100-µg dose levels were consistent with those protective in the mouse challenge model.

Based on the interim phase I results, the Moderna-led phase II effort will be amended to study two dose levels, 50 µg and 100 µg, so that a dose can be chosen for pivotal studies. Also, the NIH-led phase I effort is being amended to include a 50-µg dose level cohort across each of the three age groups. Moderna expects the phase III dose will land between 25 µg and 100 µg, and the late-stage work is slated to start in July.

Many players crowd the field in the push for a COVID-19 vaccine. J.P. Morgan analyst Cory Kasimov likes Moderna’s progress with mRNA technology. “While there’s still a long way to go and plenty of risk to navigate,” he wrote in a report, the latest findings suggest the company “is on the right track.”