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Antibody responses to Moderna's COVID-19 vaccine candidate, mRNA-1273, remained strong for almost 4 months following vaccination, data from a phase I trial indicated.

Serum neutralizing antibodies were detected in 34 healthy adult volunteers at day 119 following the first dose, and 90 days following the second dose, reported Alicia Widge, MD, of the National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Maryland, and colleagues.

Moreover, both binding and neutralizing geometric mean titers exceeded those in 41 healthy controls who were recovering from COVID-19, the authors wrote in a Correspondence piece in the

"Although correlates of protection against SARS-CoV-2 infection in humans are not yet established, these results show [...] mRNA-1273 has the potential to provide durable humoral immunity," the researchers wrote.

Importantly, they also found no new adverse events considered to be related to the vaccine after day 57.

Moderna recently made news with the interim results of phase III data that found 94.5% efficacy for its COVID-19 vaccine candidate, which NIAID co-developed, versus placebo. The company has applied for emergency use authorization, and an FDA advisory committee meeting to discuss this application is slated for Dec. 17.

While researchers reported immunogenic results covering 57 days after the first vaccination, they noted "longitudinal vaccine responses is critically important." Here, 34 participants, ages 18 and older, who received the 100-μg vaccine dose, were assessed at day 119. They were stratified by age: 18-55, 56-70, and 71 and older.

Binding and neutralizing antibodies remained "elevated" in all participants 3 months following the booster vaccination, the authors said, with the highest geometric mean titers in the youngest group. Declines over time were more pronounced in the two older cohorts, which were expected and remained well above baseline.

The authors added that the vaccine also elicited primary CD4 type 1 helper T responses 43 days after vaccination, with studies of vaccine-induced B cells ongoing.

An ongoing follow-up analysis plans to assess safety and immunogenicity in these participants for 13 months, and the phase III trial is also ongoing.

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