COVID-19 Vaccine Trial Protocols and Amendment Histories

Ten pivotal COVID-19 vaccine trial protocols (Pfizer/BioNTech, Moderna, AstraZeneca, Janssen / Johnson & Johnson) with their full amendment histories extracted verbatim from each protocol PDF’s ‘Summary of Changes’ section. Sources: the PHMPT FOIA release at phmpt.org, clinicaltrials.gov, the NEJM 2020 protocol supplement, and the Internet Archive Wayback Machine. Use the menu above or the table below to jump to any trial.

Trials that did not produce planned results

Two of the ten trials in this index never produced their planned readouts — both involving understudied populations:

C4591015 (Pfizer pregnant participants) — terminated 25 October 2021 with approximately 349 of the planned 4,000 maternal participants enrolled. Pfizer concluded the placebo-controlled design could no longer be ethically continued once COVID-19 vaccines were universally recommended for pregnant individuals.
C4591024 (Pfizer immunocompromised ≥2 years) — enrollment halted before reaching target; the trial is marked ‘Completed’ on ClinicalTrials.gov as of 23 July 2023, but no peer-reviewed primary publication of its results has been issued.

Trials covered

Trial code	Sponsor	Purpose	Total entries in history	Direct PDFs available	Report
C4591001	Pfizer / BioNTech	Pivotal Phase 1/2/3 efficacy trial (initially adults 16+, later expanded to 12+); Amendments 1–20 sourced from Pfizer's Final Protocol Amendment 20 on clinicaltrials.gov	22	6	Open report →
C4591007	Pfizer / BioNTech	Pediatric efficacy/safety trial in children 6 months to <12 years	6	6	Open report →
C4591015	Pfizer / BioNTech	Maternal immunization trial — safety/immunogenicity in pregnant participants	3	1	Open report →
C4591020	Pfizer / BioNTech	Phase 4 effectiveness study in healthcare workers and household contacts	1	1	Open report →
C4591024	Pfizer / BioNTech	Phase 2b open-label safety/tolerability/immunogenicity study in immunocompromised participants ≥2 years; recruitment stopped before Amendment 5	6	1	Open report →
P201	ModernaTX	Phase 2 dose-confirmation trial of mRNA-1273	4	1	Open report →
COVE	ModernaTX	COVE — pivotal Phase 3 randomized efficacy study of mRNA-1273 in adults 18+	11	5	Open report →
D8110C00001	AstraZeneca	Pivotal Phase 3 randomized double-blind placebo-controlled efficacy trial of AZD1222 (ChAdOx1-S; Vaxzevria) in adults ≥18; ~32,400 participants across US, Chile, Peru	7	4	Open report →
ENSEMBLE	Janssen / Johnson & Johnson	Pivotal Phase 3 randomized double-blind placebo-controlled efficacy trial of single-dose Ad26.COV2.S in adults ≥18	8	4	Open report →
ENSEMBLE 2	Janssen / Johnson & Johnson	Pivotal Phase 3 randomized double-blind placebo-controlled efficacy trial of two-dose Ad26.COV2.S in adults ≥18	8	2	Open report →

Trial code

Sponsor

Purpose

Total entries
in history

Direct PDFs
available

Report

C4591001

Pfizer / BioNTech

Pivotal Phase 1/2/3 efficacy trial (initially adults 16+, later expanded to 12+); Amendments 1–20 sourced from Pfizer's Final Protocol Amendment 20 on clinicaltrials.gov

Open report →

C4591007

Pfizer / BioNTech

Pediatric efficacy/safety trial in children 6 months to <12 years

Open report →

C4591015

Pfizer / BioNTech

Maternal immunization trial — safety/immunogenicity in pregnant participants

Open report →

C4591020

Pfizer / BioNTech

Phase 4 effectiveness study in healthcare workers and household contacts

Open report →

C4591024

Pfizer / BioNTech

Phase 2b open-label safety/tolerability/immunogenicity study in immunocompromised participants ≥2 years; recruitment stopped before Amendment 5

Open report →

P201

ModernaTX

Phase 2 dose-confirmation trial of mRNA-1273

Open report →

COVE

ModernaTX

COVE — pivotal Phase 3 randomized efficacy study of mRNA-1273 in adults 18+

Open report →

D8110C00001

AstraZeneca

Pivotal Phase 3 randomized double-blind placebo-controlled efficacy trial of AZD1222 (ChAdOx1-S; Vaxzevria) in adults ≥18; ~32,400 participants across US, Chile, Peru

Open report →

ENSEMBLE

Janssen / Johnson & Johnson

Pivotal Phase 3 randomized double-blind placebo-controlled efficacy trial of single-dose Ad26.COV2.S in adults ≥18

Open report →

ENSEMBLE 2

Janssen / Johnson & Johnson

Pivotal Phase 3 randomized double-blind placebo-controlled efficacy trial of two-dose Ad26.COV2.S in adults ≥18

Open report →

Compiled from publicly-available trial-protocol PDFs hosted by the PHMPT FOIA release (phmpt.org), clinicaltrials.gov, the NEJM 2020 protocol supplement, and the Internet Archive Wayback Machine. Compiled by Marjorie Roswell. Source code and methodology: github.com/mroswell/trialprotocols. Last updated 28 June 2026.