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Can a smaller booster dose still protect against COVID-19?

NCT ID NCT05265065

Vaccine Sponsor: Murdoch Childrens Research Institute 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 Results may not be published yet.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This status has not been confirmed recently, so it may be out of date.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 27, 2026 · Last updated Jun 27, 2026

Summary

This study looked at whether a smaller (fractional) dose of the Pfizer-BioNTech COVID-19 booster works as well as the standard dose. It involved 601 healthy adults in Mongolia who had already received two doses of Sinopharm, AstraZeneca, or Sputnik vaccines 6 to 9 months earlier. The goal was to measure immune response and side effects after the booster.

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 3

Large-scale testing in a bigger group. Usually the last step before a treatment can be approved.

Participants

601 people

The number who actually took part.

Started

May 2022

Finished

Nov 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. Have completed two doses of Sinopharm, AstraZeneca or Sputnik vaccines with the recommended schedule 6 months prior to the date of enrolment 2. Willing and able to give written informed consent 3. Aged 18 years or above 4. Willing to complete the follow-up requirements of the study Exclusion Criteria: 1. Received 3 doses of COVID-19 vaccine 2. Received 2 doses of COVID-19 less than 6 months prior to the start of the trial 3. Currently on immunosuppressive medication or anti-cancer chemotherapy 4. HIV infection 5. Congenital immune deficiency syndrome 6. Has received immunoglobulin or other blood products in the 3 months prior to vaccination 7. Study staff and their relatives 8. Have a history of a severe allergic reaction to any COVID-19 vaccines or have a medical exception to receiving further COVID-19 vaccines

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Conditions

The condition(s) this trial relates to.

COVID-19

As listed by the trial registrant

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

COVID -19

Contacts and locations

Locations

  • District Health Centre

    Ulaanbaatar, Mongolia

More trials for these conditions

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