Safety and Immunogenicity of XBB.1.5-Containing mRNA Vaccines

BackgroundSubvariants of the severe acute respiratory syndrome coronavirus (SARS-CoV-2) omicron XBB-lineage have the potential to escape immunity provided by prior infection or vaccination. For Covid-19 immunizations beginning in the Fall 2023, the U.S. FDA has recommended updating to a monovalent omicron XBB.1.5-containing vaccine. MethodsIn this ongoing, phase 2/3 study participants were randomized 1:1 to receive 50-{micro}g doses of mRNA-1273.815 monovalent (50-{micro}g omicron XBB.1.5 spike mRNA) or mRNA-1273.231 bivalent (25-{micro}g omicron XBB.1.5 and 25-{micro}g omicron BA.4/BA.5 spike mRNAs) vaccines, administered as 5th doses, to adults who previously received a primary series and 3rd dose of an original mRNA coronavirus disease 2019 (Covid-19) vaccine, and a 4th dose of a bivalent (omicron BA.4/BA.5 and original SARS-CoV-2) vaccine. Interim safety and immunogenicity data 15 days post-vaccination are presented. ResultsIn April 2023, participants received mRNA-1273.815 (n=50) and mRNA-1273.231 (n=51). The median intervals from the prior dose of BA.4/BA.5-containing bivalent vaccine were 8.2 and 8.3 months for the mRNA-1273.815 and mRNA-1273.231 groups, respectively. Both vaccines increased neutralizing antibody (nAb) geometric mean titers against all variants tested at day 15 post-booster nAb compared to pre-booster levels. Geometric mean fold-rises from pre-booster titers after the monovalent booster were numerically higher against XBB.1.5, XBB.1.16 and SARS-CoV-2 (D614G) than those of the bivalent booster and were comparable against BA.4/BA.5 and BQ1.1 variants for both vaccines. The monovalent vaccine also elicited nAb responses against omicron XBB.2.3.2, EG.5.1, FL.1.5.1 and BA.2.86 that were similar to those against XBB.1.5 in a subset (n=20) of participants. The occurrence of solicited adverse reactions and unsolicited adverse events were overall similar to those previously reported for the original mRNA-1273 50-{micro}g and omicron BA.4/BA.5-containing bivalent mRNA-1273 vaccines. ConclusionIn this interim analysis, XBB.1.5-containing monovalent and bivalent vaccines elicited potent neutralizing responses against variants of the omicron XBB-lineage (XBB.1.5, XBB.1.6, XBB.2.3.2, EG.5.1, and FL.1.5.1) as well as the recently emerged BA.2.86 variant. The safety profile of the XBB.1.5-containing vaccine was consistent with those of prior vaccines. These results overall indicate that the XBB.1.5-containing mRNA-1273.815 vaccine has the potential to provide protection against these emerging variants and support the Covid-19 vaccine update in 2023-2024 to a monovalent XBB.1.5-containing vaccine.