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Does the pfizer vaccine work as well in immunosuppressed people? new study aims to find out

NCT ID NCT04780659

Vaccine Sponsor: Karolinska University Hospital 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 Results may not be published yet.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This status has not been confirmed recently, so it may be out of date.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 27, 2026 · Updated 1 time

Summary

This study looked at how well the Pfizer mRNA vaccine triggers an immune response in people with weakened immune systems compared to healthy individuals. About 539 adults received two doses of the vaccine, and researchers measured antibody levels and side effects. The goal was to see if the vaccine protects immunosuppressed people as effectively as it does others.

What this could mean

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

Active substance
Pfizer mRNA vaccine (Comirnaty)
What this could lead to
If successful, this could show that the vaccine works well in people with weakened immune systems, helping protect them from COVID-19.
What could go wrong
This is a completed Phase 4 study, so results are already known. However, immune responses may still be weaker in some immunosuppressed groups, and the study does not test long-term protection.

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.

Phase

Phase 4

Runs after approval, following long-term safety and how well the treatment works in everyday use.

Participants

539 people

The number who actually took part.

Started

Feb 2021

Finished

May 2024

Lead sponsor

Other sponsor

The registry's catch-all category, for sponsors it does not file as a company, a government agency, or a research network.

Who can take part

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

Ages

18 years and older

Sex

Anyone

Healthy volunteers

Accepted

You do not need to have the condition being studied to take part.

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: 1\. Individuals ≥18 years old 2a. In the opinion of the investigator, individuals with immunosuppressive disease who meet one of the following criteria: * Primary immunodeficiency * Human immunodeficiency virus (HIV)-infection * Allogeneic stem cell transplantation / Chimeric antigen receptor (CAR T cell) therapy * Solid organ transplant * Chronic lymphatic leukemia or 2b. In the opinion of the investigator, individuals without immunosuppressive disease or treatment without significant co-morbidity 3\. Provision of signed informed consent to participate in the study Exclusion Criteria: 1. Previous or ongoing Coronavirus Disease-19 (COVID-19). 2. Coagulation disorders, other conditions associated with prolonged bleeding time or anticoagulant treatments, which according to the investigator contraindicate intramuscular injection. Conditions which can be corrected with measures such as platelet concentrate treatments, coagulation factors or other measures for people responsible for anticoagulants are not exclusion criteria. 3. Planned to receive another vaccine within 14 days before the first dose of the study vaccine, or during the period from the first dose of the study vaccine up to 14 days after the second dose of the study vaccine, and vaccination with another vaccine which in the investigator's opinion cannot be planned outside these time periods 4. Pregnancy or breast feeding. 5. Hypersensitivity to the active substance or to any of the excipients contained in the vaccine 6. Individuals who cannot understand the informed consent. 7. Individuals who for other reasons are considered by investigators as not suitable for inclusion

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Conditions

The condition(s) this trial relates to.

B-cell chronic lymphocytic leukemia HIV infectious disease inborn error of immunity COVID-19 prevention target

As listed by the trial registrant

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

COVID19

Contacts and locations

Locations

  • Karolinska University Hospital

    Stockholm, Huddinge, 14186, Sweden

More trials for these conditions

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