Moderna's mRNA-1273 COVID-19 vaccine generates immune responses in older adults

Moderna said data published in the NEJM showed that its mRNA-1273 vaccine candidate against COVID-19 was well tolerated and generated strong immune responses in older adults. "These interim Phase I data suggest that mRNA-1273…can generate neutralising antibodies in older and elderly adults at levels comparable to those in younger adults," remarked Tal Zaks, the company's chief medical officer.

A first interim analysis from the trial was published in the NEJM in July, with results demonstrating that a two-dose vaccination schedule of mRNA-1273 induced anti–SARS-CoV-2 immune responses, including antibody and T-cell responses, in all 45 healthy volunteers aged 18 to 55 years. The trial was later expanded to include 40 older adults, with Moderna releasing interim data in August showing that the mRNA vaccine was safe and generated an immune response in 10 subjects aged 56 to 70 years, as well as in 10 elderly participants 71 years and older.

Dose-dependent immune responses

The latest findings come from a second interim analysis that included 20 adults in each of the two older cohorts who were given two injections of mRNA-1273, at either the 25-mcg or the 100-mcg dose levels, 28 days apart. Results showed that immune responses were dose-dependent, with the 100-mcg dose eliciting higher binding and neutralising antibody titers, supporting the selection of this dose for further evaluation in the Phase III COVE study.

Moderna noted that a month after the second dose, geometric mean titers for both doses of mRNA-1273 exceeded the median of those seen in convalescent sera from 41 individuals with confirmed COVID-19 diagnosis. The company added that psuedovirus neutralisation responses were observed as early as seven days after the second vaccination and were dose-dependent. Specifically, at day 43 at the 100-mcg dose level, pseudovirus neutralisation assay titers in both groups of older adults were comparable to those seen in the younger cohort of participants aged 18 to 55, and three- to four-fold higher than those seen in convalescent sera. Moderna said that the 25-mcg dose in the 56-to-70 age cohort, and the 100-mcg dose level across all age groups, elicited a strong Th1-biased CD4 T-cell response.

No serious adverse events

With regards to safety, Moderna noted that both dose levels of mRNA-1273 were generally well tolerated, with no serious adverse events reported through day 57. The drugmaker indicated that two severe solicited systemic adverse events occurred following the second vaccination, with fever in one participant in the 56-to-70 age cohort who received the 25-mcg dose, and fatigue in another subject in the 71-plus group who was given the 100-mcg dose.

Lead researcher Evan Anderson said the side effects occurred soon after receiving the vaccine and resolved quickly. "This is similar to what a lot of older adults are going to experience with the high-dose influenza vaccine," Anderson remarked.

For related analysis, read ViewPoints: Moderna milks a competitive profile for COVID-19 vaccine.

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