THE NEW VACCINE — Spikevax and Comirnaty, the Pfizer/BioNTech mRNA COVID-19 vaccine, code for the whole spike protein of SARS-CoV-2. In contrast, mNEXSPIKE codes only for the N-terminal domain and the receptor-binding domain of the spike protein of the virus (Omicron variant JN.1); these domains are the targets of most effective anti-SARS-CoV-2 antibodies.3 The more targeted vaccine formulation allows for administration of a smaller mRNA dose (10 mcg vs 50 mcg with Spikevax).

CLINICAL STUDIES — Licensure of the new vaccine was based on the results of a randomized, observer-blind noninferiority trial (available as a presentation) in 11,454 persons ≥12 years old who had previously received a primary series of a COVID-19 vaccine (adults ≥18 years old had also received at least one booster dose). Subjects received a single dose of mNEXSPIKE or Spikevax (both bivalent formulations targeting the original and BA.4/5 Omicron strains of SARS-CoV-2). After a median follow-up of 8 months, the incidence of COVID-19 occurring ≥2 weeks after immunization was 9.9% with mNEXSPIKE and 10.8% with Spikevax; mNEXSPIKE met the prespecified criteria for noninferiority to Spikevax (relative efficacy 9.3% [95% CI -6.6% to 22.8%]). Results in adults ≥65 years old were similar to those in the overall population (relative vaccine efficacy 13.5% [95% CI -7.7% to 30.6%]). Seroresponse rates and geometric mean neutralizing antibody titer levels were higher with the new vaccine.4

ADVERSE EFFECTS — In the pivotal trial, adverse effects with mNEXSPIKE were similar to those with Spikevax and included injection-site pain, fatigue, headache, myalgia, arthralgia, chills, axillary swelling or tenderness, and nausea/vomiting. Serious adverse events occurred in 0.2% of patients who received mNEXSPIKE and in 0.3% of those who received Spikevax; no cases of myocarditis or pericarditis were reported with either vaccine.4

PREGNANCY AND LACTATION — The new vaccine has not been studied in pregnant women. In female rats, administration of an 80-mcg dose of mNEXSPIKE (8 times the recommended human dose) twice before mating and twice during gestation was not associated with impaired fertility or fetal harm. Administration of COVID-19 vaccines to nursing mothers is considered safe.5 The American College of Obstetricians and Gynecologists has recommended that all pregnant and breastfeeding women be vaccinated against COVID-19.6

DOSAGE, ADMINISTRATION, AND AVAILABILITY —The mNEXSPIKE vaccine is supplied in 10 mcg/0.2 mL prefilled syringes. The recommended dosage is a single 10-mcg intramuscular injection; mNEXSPIKE should not be given within 2 months after another COVID-19 vaccine. The syringes should be frozen during storage; after thawing, they can be kept in a refrigerator for up to 90 days or at room temperature for up to 24 hours (Spikevax can be refrigerated for up to 60 days or kept at room temperature for up to 12 hours after thawing). According to the manufacturer, mNEXSPIKE is expected to be available in the US for the 2025-2026 respiratory virus season.2