Researchers in the USA have conducted a pre-clinical study that demonstrated the efficacy of two updated versions of the Moderna mRNA-1273 vaccine against variants of SARS-CoV-2. The updated vaccine candidates include the monovalent mRNA-1273.351, which is designed to target the B.1.351 variant that emerged in South Africa, and the multivalent mRNA1273.211, which comprises a mixture of the original mRNA-1273 vaccine and mRNA-1273.351. The results of the study are published on a pre-print server.
The vaccines were evaluated in mice as both a primary vaccination series and as a booster dose among animals that had previously been immunized with two doses of mRNA-1273. The monovalent mRNA-1273.351 vaccine encodes the spike protein found in the B.1.351 lineage, while the multivalent mRNA-1273.211 comprises a 1:1 mix of mRNA-1273.351 and mRNA-1273. The original mRNA-1273 vaccine targets the ancestral wild-type virus (Wuhan-Hu-1 variant) that contains a mutation called D614G. The vaccines were administered in mice as a two-dose primary series and their immunogenicity against D614G and B.1.351 pseudoviruses was evaluated 2 weeks following the first and second immunizations. Vaccine mRNA-1273.351 elicited approximately 4-fold higher neutralization titers against B.1.351 than against D614G.
Vaccine mRNA-1273.211, on the other hand, elicited robust neutralization responses against both D614G and B.1.351, with no significant difference observed in neutralization titers. The researchers also tested the ability of mRNA-1273.351 to serve as a booster shot for neutralization against both D614G and B.1.351. Mice were injected with mRNA-1273 on days 1 and 22 and then evaluated for antibody responses over 7 months before being vaccinated a third time with mRNA-1273.351. Following this booster injection, neutralization titers against D614G increased 4.5-fold, while titers against B.1.351 increased 15-fold.
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