Moderna’s COVID-19 Vaccine Phase 1 Data Shows Rapid and Strong Immune Responses Against SARS-CoV-2

Moderna, Inc. (Cambridge, MA, USA) has announced positive interim results from the Phase 1 Study of its mRNA vaccine against COVID-19.

Moderna has published an interim analysis of the open-label Phase 1 study of mRNA-1273, its COVID-19 vaccine candidate, led by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH). The interim analysis evaluated a two-dose vaccination schedule of mRNA-1273 given 28 days apart across three dose levels (25, 100, 250 µg) in 45 healthy adult participants ages 18-55 years, and reports results through Day 57. Results from participants in the initial dose cohorts who received both vaccinations and were evaluated at pre-specified timepoints reaffirm the positive interim data assessment announced on May 18 and show that mRNA-1273 induced rapid and strong immune responses against SARS-CoV-2.


mRNA-1273 was generally safe and well-tolerated, with no serious adverse events reported through Day 57. Adverse events were generally transient and mild to moderate in severity. The most notable adverse events were seen at the 250 µg dose level, with three of those 14 participants (21%) reporting one or more severe events. Solicited systemic adverse events were more common after the second vaccination and occurred in seven of 13 (54%) participants in the 25 µg group, all 15 participants in the 100 µg group and all 14 participants in the 250 µg group. The most commonly reported systemic adverse events following second vaccination at the 100 µg dose were fatigue (80%), chills (80%), headache (60%) and myalgia (53%), all of which were transient and mild or moderate in severity. The most common solicited local adverse event at the 100 µg dose was pain at the injection site (100%), which was also transient and mild or moderate in severity. Evaluation of clinical safety laboratory values grade 2 or higher and unsolicited adverse events revealed no patterns of concern.

mRNA-1273 induced binding antibodies to the full-length SARS-CoV-2 Spike protein (S) in all participants after the first vaccination, with all participants seroconverting by Day 15. Dose dependent increases in binding titers were seen across the three dose levels, and between prime and boost vaccinations within the dose cohorts. After two vaccinations, at Day 57, geometric mean titers exceeded those seen in convalescent sera obtained from 38 individuals with confirmed COVID-19 diagnosis. Of the 38 individuals in the convalescent sera group, 15% were classified as having severe symptoms (hospitalization requiring intensive care and/or ventilation), 22% had moderate symptoms and 63% had mild symptoms. Convalescent sera samples were tested using the same assays as the study samples.

Neutralizing activity was assessed in two different assays, a live SARS-CoV-2 plaque-reduction neutralization test (PRNT) and a pseudovirus neutralization assay (pseudotyped lentivirus reporter single-round-of-infection neutralization assay, PsVNA). No participants had detectable live SARS-CoV-2 virus neutralization or PsVNA responses prior to vaccination. After two vaccinations, mRNA-1273 elicited robust neutralizing antibody titers. At Day 43, neutralizing activity against SARS-CoV-2 (PRNT80) was seen in all evaluated participants. At the Phase 3 selected dose of 100 µg, the geometric mean titer levels were 4.1-fold above those seen in reference convalescent sera.

After the second vaccination, PsVNA neutralizing antibody titers were detected in all participants in all dose cohorts. The Day 57 geometric mean titers at the 100 µg dose were 2.1-fold higher than those seen in convalescent sera. Strong correlations were observed between the binding and neutralization assays, and between the live virus and pseudovirus neutralization assays. A clear dose response was seen in geometric mean titers between the 25 µg and 100 µg dose levels, with minimal additional increases at the 250 µg dose. T-cell responses were also evaluated at the 25 µg and 100 µg dose levels. Following second vaccination, mRNA-1273 elicited Th1-biased CD4 T-cell responses without significant elevation of Th2-biased CD4 T-cell responses.

Evaluation of the durability of immune responses is ongoing, and participants will be followed for one year after the second vaccination, with scheduled blood collections throughout that period. An additional seven cohorts in this Phase 1 study have completed enrollment: a 50 µg cohort in adults 18-55, three cohorts of older adults (ages 56-70, 25 µg, 50 µg, and 100 µg) and three cohorts of elderly adults (ages 71 and above, 25 µg, 50 µg, and 100 µg). These data are expected to be published separately. Given the increased morbidity and mortality of COVID-19 in older and elderly adults, additional evidence for the potential of a vaccine to protect this population is an urgent priority.

“These Phase 1 data demonstrate that vaccination with mRNA-1273 elicits a robust immune response across all dose levels and clearly support the choice of 100 µg in a prime and boost regimen as the optimal dose for the Phase 3 study,” said Tal Zaks, M.D., Ph.D., Chief Medical Officer of Moderna. “We look forward to beginning our Phase 3 study of mRNA-1273 this month to demonstrate our vaccine’s ability to significantly reduce the risk of COVID-19 disease.”

“These positive Phase 1 data are encouraging and represent an important step forward in the clinical development of mRNA-1273, our vaccine candidate against COVID-19, and we thank the NIH for their ongoing collaboration. The Moderna team continues to focus on starting our Phase 3 study this month and, if successful, filing a BLA,” said Stéphane Bancel, Chief Executive Officer of Moderna. “We are committed to advancing the clinical development of mRNA-1273 as quickly and safely as possible while investing to scale up manufacturing so that we can help address this global health emergency.”

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