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Nearly 20 million people studied: does the COVID vaccine still hold up?

NCT ID NCT06199934

Knowledge-focused Sponsor: Pfizer Source: ClinicalTrials.gov ↗

What the study statuses mean

This study's is highlighted.

Recruitment status, easiest to join first

Recruiting now
This trial is taking on new participants right now.
Not yet recruiting
Registered, but not yet taking participants.
By invitation only
Not open to general applications. Only people the study team invites can take part.
Paused
Paused for now. It may or may not start again.
Ongoing
Running, but no longer taking on new participants.
Completed This study
The trial has finished. Results may not be published yet.
Stopped early
Stopped early, before it reached the end. That can be for many reasons, including safety.
Cancelled
Cancelled before anyone took part.

Expanded access (not trials)

Expanded access
Not a trial. This treatment can be requested outside a study, case by case, for people who qualify.
Expanded access (paused)
Not a trial. The treatment can normally be requested outside a study, but is unavailable right now.
Expanded access (ended)
Not a trial. The treatment could once be requested outside a study, but no longer can.
Approved
The treatment has been approved, so it is available normally rather than through this programme.

When the status isn't known

Details not published
The full record has not been published yet, so there is little to show here.
Status unknown
This status has not been confirmed recently, so it may be out of date.

First seen Jun 26, 2026 · Last updated Jun 26, 2026

Summary

This study looked at data from nearly 20 million people in California and Louisiana to see how well different versions of Pfizer's COVID-19 vaccine prevented severe illness, hospitalization, and death. Instead of enrolling new volunteers, researchers used existing health records and vaccine registries. The goal was to understand the vaccine's real-world effectiveness over time.

What this could mean

Our plain-language read of the trial. This is informational only, not medical advice or a prediction.

Active substance
BNT162b2 (Pfizer-BioNTech COVID-19 vaccine)
What this could lead to
If successful, this study could confirm how well updated COVID-19 vaccines work in real-world settings, helping guide future vaccination strategies.
What could go wrong
This is an observational study using existing data, not a controlled trial, so results may be affected by unmeasured factors. It cannot prove cause and effect.

This is an AI summary of the original study and may miss details. Read our disclaimer.

Study facts

What this study's own registry entry says, in plain language.

Participants

19,853,610 people

The number who actually took part.

Started

Sep 2023

Finished

Jul 2024

Lead sponsor

A company

The lead sponsor is a pharmaceutical, biotech, or medical-device company.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Who is studied

Patients who were California or Louisiana residents in the HealthVerity claims database will be defined using the following hierarchical definition: 1. Persons who have their enrollment file record indicating a patient location of California or Louisiana in HealthVerity claims enrollment file. 2. Persons who have a patient state location other than California or Louisiana in HealthVerity claims enrollment but have one or more records in the California or Louisiana Immunization Registry. Examples include people who previously lived in Texas but moved to California and received a vaccine, or persons who crossed state lines for a vaccine and remain in their non-California state in claims data.

Ages

Children (under 18), adults (18 to 64) and older adults (65 and over)

Sex

Anyone

Healthy volunteers

Not accepted

This study is not open to healthy volunteers. The entry requirements below say who it is open to.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * People with at least one year of pharmacy and medical enrollment in HealthVerity prior to vaccine availability * State of California or Louisiana resident for at least one year Exclusion criteria: * People currently pregnant, * Individuals with discrepancies in sex and/or year of birth between HealthVerity claims and California/Louisiana immunization registry datasets * A diagnosis of COVID-19 in any setting ≤ 90 days prior to start of study or receipt COVID-19 vaccine ≤ 90 days prior to start of study.

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Conditions

The condition(s) this trial relates to.

COVID-19 prevention target

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

COVID-19 vaccines SARS-CoV-2

Contacts and locations

Locations

  • Pfizer Global Headquarters

    New York, New York, 10001, United States

More trials for these conditions

Other studies related to the condition(s) this trial covers.