Moderna’s investigational coronavirus disease 2019 (COVID-19) vaccine candidate, mRNA-1273, was found to be generally well tolerated and elicited neutralizing antibody activity in all study participants, according to interim phase 1 data published in The New England Journal of Medicine.

The open-label, dose escalation study assessed the safety and immunogenicity of mRNA-1273 in 45 healthy adults aged 18 to 55 years. Participants received 1 of 3 doses of mRNA-1273 (25, 100, or 250mcg) administered intramuscularly on a 2-dose vaccination schedule, given 28 days apart. The study is being led by the National Institute of Allergy and Infectious Diseases (NIAID).

The interim analysis confirmed the positive data announced in May 2020. Results showed that mRNA-1273 induced rapid and strong immune responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Dose dependent increases in immunogenicity were observed across all 3 dose levels and between prime and boost doses within the dose cohorts. 

“After the first vaccination, antibody responses were higher with higher dose (day 29 enzyme-linked immunosorbent assay anti–S-2P antibody geometric mean titer [GMT], 40,227 in the 25μg group, 109,209 in the 100μg group, and 213,526 in the 250μg group). After the second vaccination, the titers increased (day 57 GMT, 299,751, 782,719, and 1,192,154, respectively),” the study authors reported. Participants demonstrated high levels of neutralizing antibody activity that exceeded those seen in convalescent sera obtained from persons with confirmed COVID-19.

Regarding safety, mRNA-1273 was generally safe and well tolerated, with no serious adverse events reported through day 57. More than half of the participants reported fatigue, headache, chills, myalgia or pain at the injection site. Systemic adverse events were more common after the second vaccination, particularly with the highest dose, and 3 participants (21%) in the 250mcg dose group reported 1 or more severe adverse events.

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“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 100µg in a prime and boost regimen as the optimal dose for the phase 3 study,” said Tal Zaks, MD, PhD, 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.”

Further analysis of an additional 7 cohorts will provide more information on immune responses in older adults and elderly individuals, populations that are at increased risk of morbidity and mortality. Data from this analysis will be published separately. The Company also announced full enrollment in a phase 2 trial of mRNA-1273, which includes 300 participants aged 18-55 years and 300 participants 55 years and older. Plans are also underway to begin a phase 3 efficacy trial of the vaccine candidate on July 27, 2020.

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