How did the efficacy of Pfizer-BioNTech and Moderna vaccines compare across age groups in 2020 trials?
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Executive summary
The Phase 3 trials reported in late 2020 showed near-identical high efficacy for the two mRNA vaccines in adults — Pfizer‑BioNTech’s BNT162b2 at about 95% and Moderna’s mRNA‑1273 at roughly 94–95% — but age‑specific data diverged where companies ran separate pediatric protocols and where later observational studies examined older adults, leaving nuance outside the headline numbers [1] [2] [3].
1. Adults: virtually the same headline efficacy in the original trials
Both companies’ pivotal late‑2020 Phase 3 results gave nearly indistinguishable point estimates for prevention of symptomatic COVID‑19 in adults — Pfizer reported 95% efficacy from a trial of about 43,000 participants and Moderna reported about 94.1% (often rounded to 95%) — and those figures drove the emergency authorizations in December 2020 [1] [2] [3].
2. Adolescents: Pfizer’s trial showed a clear signal, Moderna followed with separate data later
Pfizer’s adolescent Phase 1/2/3 data announced strong protection — a 100% efficacy estimate in 12–15‑year‑olds in the reported analysis with more than 2,000 participants — a result Pfizer emphasized in its follow‑up releases to regulators [1] [4]. Moderna also moved into younger age trials and reported robust immune responses, but the public comparisons from 2020–2021 make Pfizer’s 12–15 result the clearest early pediatric efficacy headline in the sources provided [1] [4].
3. Young children: different dosing choices changed trial outcomes
In the youngest cohorts the two vaccines were not directly comparable because companies used different doses and schedules; Moderna’s two‑dose regimen in 6–23‑month‑olds showed modest efficacy (about 50.6% in that age band and lower in 2–5 year olds), whereas Pfizer’s three‑dose program for the same age range produced too few cases in trials to support a reliable point estimate, leaving regulators to rely more heavily on immunobridging and safety data [5].
4. Older adults: trial signals plus later observational data favor Moderna modestly
Although the original trials showed high efficacy across adult age strata, later large observational and comparative studies — including a Veterans Affairs emulation and analyses of millions of vaccinated older adults — have suggested that Moderna-vaccinated older adults experienced slightly lower rates of symptomatic infection and hospitalization than Pfizer recipients in real‑world follow‑up; a Brown University analysis and VA studies reported a modest advantage for Moderna in older populations [6] [7] [8] [9].
5. Limitations, comparability caveats, and why “95% vs 94%” misleads
Direct head‑to‑head randomized comparisons were not conducted in the Phase 3 programs, trial endpoints and case definitions varied, and the small differences in point estimates are within the statistical and methodological uncertainty of separate trials; real‑world effectiveness evolves with variants and waning immunity, so later observational work — which introduces its own biases — has been relied upon to probe age‑stratified differences [7] [8] [10].
6. Motives, messaging and how the narrative formed
Early public messaging emphasized round numbers (95% vs 94.1%) because those were pivotal for authorization and public confidence; manufacturers and press releases highlighted strongest subgroup results (for example Pfizer’s adolescent 100% headline), while independent researchers later mined large health systems for comparative effectiveness in older adults, producing a narrative that Moderna may be marginally more durable in seniors — an interpretation supported by some observational studies but not proven by randomized head‑to‑head trials [4] [6] [8].
7. Bottom line for interpreting 2020-era age comparisons
For adults in the 2020 pivotal trials the vaccines were effectively equivalent at preventing symptomatic COVID‑19, while pediatric outcomes diverged because of distinct dosing paths and sample sizes (Pfizer’s clear adolescent result; Moderna’s measurable but lower efficacy in very young children), and later real‑world analyses suggest a modest Moderna advantage in older adults — a pattern that is plausible but not conclusively established by randomized evidence [1] [2] [5] [6] [8].