The study analyzed 33 healthy adult participants in the U.S. National Institute of Health-led phase I study of Moderna's COVID-19 vaccine at six months following a second 100 µg dose (day 209). Antibody decay was estimated using two approaches and was consistent with published observations of convalescent patients with COVID-19 through eight months after symptom onset, the company said in a statement.

Studies monitoring immune responses beyond six months are ongoing. Out of an abundance of caution, Moderna is also pursuing a clinical development strategy against emerging variants.

Additionally, the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), will conduct a phase I clinical trial to assess the company's monovalent and multivalent modified mRNA-1273 vaccines as a primary series in naive individuals and as a booster vaccine in those previously vaccine with mRNA-1273.