A Redesigned, Lower-Dose COVID Vaccine Protected as Well as the Original

CATEGORY: IMMUNE HEALTH

The redesigned shot didn’t lose a step. Moderna’s next-generation COVID vaccine, built around one-fifth the dose of the original, protected people against symptomatic infection just as well as the formula the world already knows, in a head-to-head trial of 11,454 people aged 12 and up.¹ Antibody levels actually came back a bit higher on the smaller dose. Arms hurt less, too. The new vaccine, sold as mNEXSPIKE, was approved in the US in May 2025 for adults 65 and older and for younger people with at least one condition that raises their risk.

Two Shots Enter, Nobody Knows Which

Participants across the US, UK and Canada were randomly dealt either the new vaccine or the original, and the people assessing their health didn’t know who got what. The trial then counted lab-confirmed symptomatic COVID cases through the 2023 season. Relative protection landed 9.3% in the new shot’s favor, with a margin of error wide enough that the true difference could be zero.¹ That still counts as success here. The goal was never to win against the original, only to prove the slimmer dose gives up nothing. Among adults 65 and older, the numbers tilted further toward the new vaccine, again without reaching statistical certainty.¹

Why Shrink a Vaccine That Already Works

Standard mRNA vaccines hand your cells the blueprint for the virus’s entire spike protein. The blueprint in this one is trimmed to the spike’s two most useful regions, the parts antibodies actually grab. Think of a wanted poster cropped to the face. Nothing else earns the ink. Less mRNA per dose means a gentler load on the arm that receives it: pain at the injection site was the most common complaint with both vaccines, but less frequent with the new one.¹ Measured antibodies ran about 1.2 to 1.3 times the original’s level, and in the group where protection matters most, people 65 and older, the immune response was stronger across the board.¹ Moderna funded and ran the trial, as is typical for vaccine licensing studies.

Key Takeaways

• Protection against symptomatic COVID was equivalent between the new 10-microgram vaccine and the original 50-microgram version over a full season, which is what the trial was designed to prove.
• The redesigned shot produced somewhat higher antibody levels and fewer sore arms, with the clearest immune advantage in people 65 and older.
• The hint of better protection did not reach statistical significance, so the honest claim is a match, not a win.
• It’s approved in the US for people 65 and older, and for ages 12 to 64 with a risk condition.

References

1. Chalkias S, Dennis P, Petersen D, et al. Efficacy, immunogenicity, and safety of a next-generation mRNA-1283 COVID-19 vaccine compared with the mRNA-1273 vaccine (NextCOVE): results from a phase 3, randomised, observer-blind, active-controlled trial. The Lancet Infectious Diseases. 2025; published online July 7. doi:10.1016/S1473-3099(25)00236-1. link