Moderna announced the publication of the second interim analysis of the open-label Phase 1 study of mRNA-1273, its vaccine candidate against COVID-19, in The New England Journal of Medicine. This interim analysis evaluated a two-dose vaccination schedule of mRNA-1273 given 28 days apart in 40 healthy adult participants across two dose levels (25 and 100 μg) in two age cohorts (ages 56-70 and ages 71+) and reports results through Day 57 (one month after the second dose). This analysis found that both the 25 μg and 100 μg dose levels were generally well-tolerated in both age cohorts. Immune responses were dose-dependent with the 100 μg dose eliciting higher binding and neutralising antibody titers, supporting the selection of the 100 μg dose for further study in the Phase 3 trial. The study was led by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH).

“These interim Phase 1 data suggests that mRNA-1273, our vaccine candidate for the prevention of COVID-19, can generate neutralising antibodies in older and elderly adults at levels comparable to those in younger adults. Given the increased morbidity and mortality of COVID-19 in older and elderly adults, these data give us optimism in demonstrating mRNA-1273’s protection in this population, which is being evaluated in the Phase 3 COVE study,” said Tal Zaks, Chief Medical Officer of Moderna.

Both the 25 μg and 100 μg dose levels of mRNA-1273 were generally well-tolerated, with no serious adverse events reported through Day 57. The most common solicited adverse events were headache, fatigue, myalgia, chills, and pain at the injection site, the majority of which were mild-to-moderate in severity and of self-limited duration. Local and systemic reactogenicity were more common and more frequently moderate in severity after the second dose. Two severe solicited systemic adverse events occurred following the second vaccination: fever in one participant in the ages 56-70 cohort who received the 25 μg dose and fatigue in one participant in the ages 71+ cohort who received the 100 μg dose. Clinical laboratory values of Grade 2 or higher revealed no pattern of concern. Participants will continue to be followed through 13-months to allow for a longer assessment of vaccine-related adverse events.

At both the 25 μg and 100 μg dose levels, after two vaccinations, mRNA-1273 induced dose-dependent binding antibody responses reaching the upper quartile of the distribution of convalescent sera. At Day 57 (1-month post-dose 2), geometric mean titers (GMT) exceeded the median of those seen in convalescent sera from 41 individuals with confirmed COVID-19 diagnosis.

Neutralising activity was assessed with multiple assays, including a pseudovirus neutralisation assay (pseudotyped lentivirus reporter single-round-of-infection neutralisation assay [PsVNA]) against the two most common SARS-CoV-2 variants (614D and 614G) and three live-virus neutralisation assays (SARS-CoV-2 nanoluciferase high-throughput neutralisation assay [nLUC HTNA], focus reduction neutralisation test mNeonGreen [FRNT-mNG] and classical plaque-reduction neutralisation test [PRNT]). No participants had detectable neutralising responses by any assay prior to vaccination, and robust neutralising activity was observed in all participants 14 days after the second vaccination.

Psuedovirus neutralisation responses were observed as early as seven days after the second vaccination and were dose-dependent across all age groups (18-55, 56-70 and 71+). At Day 43 at the 100 μg dose level, PsVNA ID50 titers in the older adult cohorts ages 56-70 (GMT 402) and 71+ (GMT 317) were comparable to those seen in the age 18-55 cohort (GMT 360), and 3- to 4-fold higher than those seen in convalescent sera (GMT 106). Titers remained high through four weeks after the second dose in all age cohorts. Neutralizing activity against the 614G variant was also observed at the 100 μg dose in all age cohorts.

Results were consistent using three live virus assays. Neutralising antibody titers as measured by nLUC HTNA and FRNT-mNG were similar across all age groups (18-55, 56-70 and 71+). At Day 43, PRNT80 GMT in the 100 ug dose groups was 878 in the 56-70 and 317 in the 71+ age cohort, representing 5.5 and 2.0-fold above convalescent sera respectively, and 4.1-fold above convalescent sera in the 18-55 age group (GMT 654).

The 25 μg dose in the 56-70 age cohort and the 100 μg dose level across all age groups (18-55, 56-70 and 71+) elicited a strong Th1-biased CD4 T cell response.

The US government has purchased 100 million doses of mRNA-1273, with an option to purchase an additional 400 million doses.