11 March 2021 - - The first participants have been dosed with US-based biotechnology company Moderna, Inc's (NASDAQ: MRNA) modified COVID-19 vaccines, designed to address the potential need for booster vaccine candidates, in an amendment to the ongoing Phase 2 clinical study, the company said.

mRNA-1273.351 encodes for the prefusion stabilized Spike protein of the SARS-CoV-2 variant B.1.351, first identified in the Republic of South Africa, and is being assessed as a booster vaccine to increase the breadth of response to emerging variants with key-receptor-binding domains mutations.

mRNA-1273.211 is a multivalent candidate which combines mRNA-1273, Moderna's authorized vaccine against ancestral strains, and mRNA-1273.351 in a single vaccine, designed to elicit a broad immune response as both a primary series and when administered as a boost to those who have previously received mRNA-1273.

Previously published data has shown that vaccination with the Moderna COVID-19 Vaccine produced neutralizing titers against all key variants tested, including B.1.1.7, first identified in the UK, and B.1.351, with a 6-fold reduction in neutralizing titers against B.1.351.

Moderna said that, out of an abundance of caution, it is pursuing a clinical development strategy against these emerging variants.

An amendment to the Phase 2 study will enroll 60 participants previously vaccinated with mRNA-1273 to receive a single booster dose of either 20 µg of a variant-specific booster candidate, mRNA-1273.351, based on the B.1.351 variant first identified in the Republic of South Africa; 50 µg of mRNA-1273.351; and 50 µg of a multivalent booster candidate, mRNA-1273.211, which combines mRNA-1273, Moderna's authorized vaccine against ancestral strains, and mRNA-1273.351 in a single vaccine.

In a previous protocol amendment, Phase 2 study participants vaccinated with mRNA-1273 have been offered a single 50 µg booster dose of mRNA-1273.

Dosing in this protocol extension is ongoing.

In parallel, NIAID, part of the National Institutes of Health, will conduct a Phase 1 clinical trial to assess the monovalent and multivalent modified mRNA-1273 vaccines as a primary series in naïve individuals and as a booster vaccine in those previously vaccine with mRNA-1273.

NIAID will initiate this study after receiving safe-to-proceed authorization from the FDA. NIAID will provide additional information when the trial begins.

The clinicaltrials.gov identifier is NCT04785144.

The Moderna COVID-19 Vaccine is an mRNA vaccine against COVID-19 encoding for a prefusion stabilized form of the Spike (S) protein, which was co-developed by Moderna and investigators from the National Institute of Allergy and Infectious Disease's (NIAID) Vaccine Research Center.

The first clinical batch, which was funded by the Coalition for Epidemic Preparedness Innovations, was completed on February 7, 2020 and underwent analytical testing; it was shipped to the National Institutes of Health on February 24, 2020, 42 days from sequence selection.

The first participant in the NIAID-led Phase 1 study of the Moderna COVID-19 Vaccine was dosed on March 16, 2020, 63 days from sequence selection to Phase 1 study dosing.