The manuscript has been submitted as a preprint to bioRxiv and will be submitted for peer-reviewed publication.

The two-dose regimen of the Moderna COVID-19 vaccine at the 100 µg dose is expected to be protective against emerging strains detected to date. Nonetheless, Moderna announced its clinical strategy to proactively address the pandemic as the virus continues to evolve.

• The Company will test an additional booster dose of its COVID-19 vaccine, mRNA-1273, to study the ability to further increase neutralizing titers against emerging strains beyond the existing primary vaccination series.
• The Company is advancing an emerging variant booster candidate, mRNA-1273.351, against the B.1.351 variant first identified in the Republic of South Africa.
• The Company is advancing mRNA-1273.351 into preclinical studies and a Phase 1 study in the U.S. to evaluate the immunological benefit of boosting with strain-specific spike proteins. 

Moderna expects that its mRNA-based booster vaccine (whether mRNA-1273 or mRNA-1273.351) will be able to further boost neutralizing titers in combination with all of the leading vaccine candidates.

From the CEO of Moderna

Stéphane Bancel, Chief Executive Officer of Moderna, explained, “As we seek to defeat the COVID-19 virus, which has created a worldwide pandemic, we believe it is imperative to be proactive as the virus evolves. We are encouraged by these new data, which reinforce our confidence that the Moderna COVID-19 Vaccine should be protective against these newly detected variants. Out of an abundance of caution and leveraging the flexibility of our mRNA platform, we are advancing an emerging variant booster candidate against the variant first identified in the Republic of South Africa into the clinic to determine if it will be more effective to boost titers against this and potentially future variants.”

First detected in September 2020 in the United Kingdom, the SARS-CoV-2 B.1.1.7 variant has seventeen mutations in the viral genome with eight mutations located in the spike (S) protein. The B.1.351 variant, first detected in South Africa, has ten mutations located in the spike (S) protein. Both variants have spread at a rapid rate and are associated with increased transmission and a higher viral burden after infection.

The in vitro study assessed the ability of mRNA-1273 to elicit potently neutralizing antibodies against the new SARS-CoV-2 (the virus that causes COVID-19) variants, using sera from eight Phase 1 clinical trial participants (aged 18-55 years) who received two 100 µg doses of mRNA-1273 and separately using sera from non-human primates (NHPs) immunized with two doses of 30 µg or 100 µg of mRNA-1273.

For the B.1.1.7 variant, neutralizing antibody titers remained high and were generally consistent with neutralizing titers relative to prior variants. No significant impact on neutralization was observed from either the full set of mutations found in the B.1.1.7 variant or from specific key mutations of concern. Although these mutations have been reported to lessen neutralization from convalescent sera and to increase infectivity, sera from the Phase 1 participants and NHPs immunized with mRNA-1273 were able to neutralize the B.1.1.7 variant to the same level as prior variants.

For the B.1.351 variant, vaccination with the Moderna COVID-19 vaccine produces neutralizing antibody titers that remain above the neutralizing titers that were shown to protect NHPs against wildtype viral challenge.

While the Company expects these levels of neutralizing antibodies to be protective, pseudovirus neutralizing antibody titers were approximately 6-fold lower relative to prior variants. These lower titers may suggest a potential risk of the earlier waning of immunity to the new B.1.351 strains.

Prohost Observations 

This is comforting news.

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