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A booster dose of Moderna's bivalent vaccine candidate was well-tolerated and produced a superior immune response against a wide variety of variants, including Omicron and Delta, compared with the current single-valent booster, the manufacturer .

Moderna said that a 50 μg dose of mRNA-1273.211 -- which targets the ancestral SARS-CoV-2 strain along with mutations found in the Beta variant -- was superior against the Beta, Delta, and Omicron variants at 1 month following a booster dose, as well as at 6 months against Beta and Omicron.

The company noted that several of these mutations "have been persistent in more recent variants of concern including Omicron."

"The results indicate that mRNA-1273.211 at the 50 µg dose level induced higher antibody responses than the 50 µg mRNA-1273 booster, even when additional variants of concern were not included in the booster vaccine," said Moderna CEO Stéphane Bancel, in a statement.

Bancel also touted a second bivalent booster candidate -- mRNA-1273.214, which combines the ancestral strain with an Omicron-specific booster -- as the company's "lead candidate for the fall 2022 Northern Hemisphere booster​," with data expected later in the second quarter of this year.

"We believe that a bivalent booster vaccine, if authorized, would create a new tool as we continue to respond to emerging variants," he said.

Data on the Beta-targeted booster came from 300 people in an , with . Adult participants were from Moderna's original phase III trial, who received their first booster dose 9 to 10 months after their primary series. Antibody responses were higher against the ancestral strain, Beta, Delta, and Omicron variants at 28 days after the bivalent booster than with the single-valent booster, and were higher against the ancestral strain, Beta, and Omicron at 180 days later.

"Immunogenicity objectives were met," the authors said, and Moderna added that the bivalent booster demonstrated a 2.20-fold (95% CI 1.74-2.79) increase in neutralizing antibody response against Omicron at 1 month and a 2.15-fold (95% CI 1.66-2.78) increase at 6 months versus Moderna's authorized booster.

The bivalent booster was well-tolerated, with similar incidence of solicited and unsolicited adverse events compared with the authorized booster. Moderna also noted that 595 people in the trial received a 100 μg dose of the bivalent booster, which was "generally well-tolerated."

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