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A Feb. 24 press release from Moderna about its booster (mRNA-1273.351) that covers the South Africa variant indicated it had shipped doses to the NIH for a Phase 1 trial.
Quote:Moderna plans to evaluate three approaches to boosting, including:
  • A variant-specific booster candidate, mRNA-1273.351, based on the B.1.351 variant first identified in the Republic of South Africa, at the 50 µg dose level and lower.
  • 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 at the 50 µg dose level and lower.
  • A third dose of mRNA-1273, the Moderna COVID-19 Vaccine, as a booster at the 50 µg dose level. The Company has already begun dosing this cohort with the booster.
On Mar. 10, Moderna indicated first participants were dosed in a Phase 2 trial for the booster candidates.

On May 5, Moderna indicated "positive initial booster data" from the Phase 2 trail.
Quote:a single 50 µg dose of mRNA-1273 or mRNA-1273.351 given as a booster to previously vaccinated individuals increased neutralizing antibody titer responses against SARS-CoV-2 and two variants of concern, B.1.351 (first identified in South Africa) and P.1 (first identified in Brazil). A booster dose of mRNA-1273.351, the Company’s strain-matched booster, achieved higher neutralizing antibody titers against the B.1.351 variant of concern than a booster dose of mRNA-1273.

I read that as saying a third dose of Moderna increased antibodies for the virus and both variants.  An alternative dose of their formula for B.1.351 did better against that (but they don't say it did better against P.1).

This suggests that the original vaccine was still effective after 6-8 months (or maybe not).

Quote:Participants in the Phase 2 study were tested for pseudovirus neutralization (PsVN) titers prior to boosting approximately 6 to 8 months after their primary vaccination series. Although titers versus the wild-type SARS-CoV-2 virus remained high, with 37 of 40 participants having detectable titers, titers against the variants of concern (B.1.351 and P.1) were much lower, with approximately half of participants having titers below the assay limit of quantification prior to boosting. Two weeks after receiving either mRNA-1273 or mRNA-1273.351, PsVN titers were boosted in all participants and all variants tested. Following boost, geometric mean titers (GMT) against the wild-type, B.1.351, and P.1 variants increased to levels similar to or higher than the previously reported peak titers against the ancestral (D614G) strain following primary vaccination.