COVID-19Phase 3NCT05265065

Evaluation of Full Versus Fractional Dose of COVID-19 Vaccine Given as a Booster for the Prevention of COVID-19 in Adults in Mongolia.

A Phase 3 study testing Tozinameran - Standard Dose and Tozinameran - Fractional Dose in people with COVID-19, run by Murdoch Childrens Research Institute at 1 site in Mongolia.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Official record

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Trial summary

This clinical trial is a single-blind, randomised study to determine the reactogenicity and immunogenicity of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) vaccine (Pfizer-BioNTech) as booster dose in adults, who have previously received either Sinopharm (BBIBP-CorV®), AstraZeneca (ChAdOx1-S, or… Read more about this study

Who is it for?: Ages 18 years and olderHealthy volunteers can take part
Conditions the study is for: COVID-19
What is being tested?: Tozinameran - Standard Dose and Tozinameran - Fractional Dose
Type of treatment: Vaccines, Injection or infusion
Could I receive a placebo?: No, everyone receives an active treatment
How many people: 601 participants
Where: 1 siteMongolia
Study dates: 27 May 2022to 6 Nov 2024
Phase: Phase 3
Are there results?: Yes, posted in the registrySummary in the doctors' view

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

Ages 18 years and older
All sexes
Healthy volunteers accepted
Adult, Older adult

Who may be able to join

Have completed two doses of Sinopharm, AstraZeneca or Sputnik vaccines with the recommended schedule 6 months prior to the date of enrolment
Willing and able to give written informed consent
Aged 18 years or above
Willing to complete the follow-up requirements of the study

Who cannot join

Received 3 doses of COVID-19 vaccine
Received 2 doses of COVID-19 less than 6 months prior to the start of the trial
Currently on immunosuppressive medication or anti-cancer chemotherapy
HIV infection
Congenital immune deficiency syndrome
Has received immunoglobulin or other blood products in the 3 months prior to vaccination
Study staff and their relatives
Have a history of a severe allergic reaction to any COVID-19 vaccines or have a medical exception to receiving further COVID-19 vaccines

Trial locations and contacts

1 site in 1 country.

Mongolia1 site

District Health Centre
Ulaanbaatar

Other trials in Mongolia

About this study

Official title: A Randomised Controlled Trial to Assess the Immunogenicity, Safety and Reactogenicity of Standard Dose Versus Fractional Doses of COVID-19 Vaccine (Pfizer-BioNTech) Given as a Booster Dose After Priming With Sinopharm, AstraZeneca or Sputnik in Healthy Adults in Mongolia

Participants are healthy adults aged 18 years or older, with no upper age limit. Procedures will be implemented to ensure participants of all ages (aged 18 and above) are included and that there is an even age distribution (<50 and ≥50 years) in each group. There will be a total of 6 groups (Sinopharm-standard dose Pfizer, Sinopharm-fractional dose Pfizer, AstraZeneca-standard dose Pfizer, AstraZeneca-fractional dose Pfizer, Sputnik - standard dose Pfizer, Sputnik - fractional dose Pfizer), with 200 participants per group for Sinopharm and 100 for AstraZeneca and Sputnik.

Read the detailed description

As per brief summary

Conditions: COVID-19
Being tested: Tozinameran - Standard Dose, Tozinameran - Fractional Dose
Keywords: Booster dose, Pfizer, fractional and standard doses, COVID-19 vaccination, mRNA vaccine
Medical subject headings: COVID-19

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

Tozinameran - Standard DoseBiological
Also called BNT162b2, Comirnaty, Pfizer Covid-19 vaccine
Tozinameran is a single-stranded, 5'-capped messenger RNA (mRNA) produced using a cellfree in vitro transcription from the corresponding DNA templates, encoding the viral spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Dose - 30 µg in 0.3 ml. Liquid for injection. Single dose.
Tozinameran - Fractional DoseBiological
Also called BNT162b2, Comirnaty, Pfizer Covid-19 vaccine
Tozinameran is a single-stranded, 5'-capped messenger RNA (mRNA) produced using a cellfree in vitro transcription from the corresponding DNA templates, encoding the viral spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Dose - 15 µg in 0.15 ml. Liquid for injection. Single dose.

Study groups in NCT05265065
Study group	Role	What they receive
Standard Pfizer-BioNTech booster group	Active comparator	Biological/Vaccine: Tozinameran - Standard Dose Other Names: BNT162b2 Comirnaty Pfizer Covid-19 vaccine Tozinameran is a single-stranded, 5'-capped messenger RNA (mRNA) produced using a cellfree in vitro transcription from the corresponding DNA templates, encoding the viral spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Dose - 30 µg in 0.3 ml. Liquid for injection. Single dose. Receives: Biological: Tozinameran - Standard Dose
Fractional Pfizer-BioNTech booster group	Experimental	Biological/Vaccine: Tozinameran - Standard Dose Other Names: BNT162b2 Comirnaty Pfizer Covid-19 vaccine Tozinameran is a single-stranded, 5'-capped messenger RNA (mRNA) produced using a cellfree in vitro transcription from the corresponding DNA templates, encoding the viral spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Dose - 15 µg in 0.3 ml. Liquid for injection. Single dose. Receives: Biological: Tozinameran - Fractional Dose

What is being measured

The primary outcome is the main question the study is designed to answer.

Seroresponse
Serum samples collected at 28-days post booster vaccination from all groups will be evaluated for SARS-CoV-2 specific IgG antibodies using IgG ELISA. The primary endpoint is the seroresponse rate at the Day-28 visit. The seroresponse rate at the individual level is defined as either a ≥4-fold rise in binding antibodies at the Day-28 visit compared to baseline (pre-vaccination) with a titre of <200 BAU/ml, a ≥2-fold rise among participants with a baseline (pre-vaccination) titre of >200 BAU/ml, or a ≥4-times the lower limit of detection if baseline levels are lower than the limit of detection.
Measured: 28-days post booster vaccination
Solicited Grade 3 or 4 Local or Systemic Reaction
Questionnaire to document solicited reactions is developed specifically for this study. Data will be reported as the proportion of participants who report grade 3 or 4 reactions by each intervention arm. Solicited reactions such as pain, tenderness, erythema/redness, induration, swelling, fever, nausea, vomiting, headache, fatigue/malaise, myalgia, arthralgia, diarrhea, enlarged lymph nodes will be collected from the participants 7 days post-vaccination.
Measured: 7 days post booster vaccination

Secondary outcomes (17)

Seroresponse by Priming Vaccine Strata
Serum samples collected at 28-days post booster vaccination from all groups will be evaluated for SARS-CoV-2 specific IgG antibodies using IgG ELISA. The primary endpoint is the seroresponse rate at the Day-28 visit. The seroresponse rate at the individual level is defined as either a ≥4-fold rise in binding antibodies at the Day-28 visit compared to baseline (pre-vaccination) with a titre of <200 BAU/ml, a ≥2-fold rise among participants with a baseline (pre-vaccination) titre of >200 BAU/ml, or a ≥4-times the lower limit of detection if baseline levels are lower than the limit of detection.
Priming strata (previously COVID vaccination): AstraZeneca (ChAdOx1-S, or Vaxzevria®); Sinopharm (BBIBP-CorV®); Sputnik V (Gam-COVID-Vac®)
Measured: 28-days post booster vaccination
SARS-CoV-2 Specific IgG Antibodies at Day-28
Serum samples collected at 28-days post booster vaccination from all groups will be evaluated for SARS-CoV-2 specific IgG antibodies using IgG ELISA.
Measured: 28-days post booster vaccination
SARS-CoV-2 Specific IgG Antibodies at Day-28 by Priming Vaccine Strata
Serum samples collected at 28-days post booster vaccination from all groups will be evaluated for SARS-CoV-2 specific IgG antibodies using IgG ELISA.
Priming strata (previously COVID vaccination): AstraZeneca (ChAdOx1-S, or Vaxzevria®); Sinopharm (BBIBP-CorV®); Sputnik V (Gam-COVID-Vac®)
Measured: 28-days post booster vaccination
SARS-CoV-2 Specific IgG Antibodies at Baseline (Pre-booster), 28 Days, 6 Months, 12 Months, 18 Months, and 24 Months Post-booster Vaccination.
Serum samples collected at baseline (pre booster), 28 days, 6 months, 12 months, 18 months, and 24 months post booster vaccination from the study arms will be evaluated for SARS-CoV-2 specific IgG antibodies using the commercial Euroimmun S1 IgG ELISA. Data will be reported as binding antibody units (BAU)/mL and presented as geometric mean concentration (GMC) and 95% confidence intervals (CI).
Measured: Baseline (pre booster), 28 days, 6 months, 12 months, 18 months, and 24 months post-booster vaccination.
SARS-CoV-2 Specific Neutralising Antibodies at Baseline (Pre-booster), 28 Days, 6 Months, 12 Months, 18 Months, and 24 Months Post-booster Vaccination Measured by Surrogate Virus Neutralisation Test (sVNT).
Serum samples collected at baseline (pre booster), 28 days-, 6- and 12-months post booster vaccination from all groups will be evaluated for SARS-CoV-2 specific neutralising antibodies using the GenScript® cPass surrogate virus neutralization test (sVNT) for both wild-type and Omicron variant. Neutralising antibody response will be reported as percentage (%) inhibition of receptor binding domain-angiotensin-converting enzyme 2 (RBD-ACE2) binding relative to a positive control.
Measured: Baseline (pre-booster), 28 days, 6 months, 12 months, 18 months, and 24 months post-booster vaccination.
SARS-CoV-2 Specific Neutralising Antibodies at Baseline (Pre Booster), 28 Days-, 6- and 12-months Post Booster Vaccination Measured by SARS-CoV-2 Microneutralisation Assay
A subset of samples (20%) from all four timepoints will be assessed using a SARS-CoV-2 microneutralisation assay to both the wild type (vaccine) strain and for two SARS-CoV-2 Variants of concern. Neutralizing antibody will be reported as endpoint titre.
Measured: Baseline (pre booster), 28 days-, 6- and 12-months post booster vaccination
Interferon Gamma (IFNγ) Concentrations in International Units (IU)/mL
IFN-γ concentrations (IU/mL) as a measure of cellular immunity will be assessed in a subset of participants. IFN-γ production will be stimulated using QuantiFERON Human IFN-γ SARS-CoV-2 (Qiagen) and quantified by ELISA. Results are summarised as geometric mean concentrations (GMCs) with 95% confidence intervals.
Measured: Baseline (pre booster), 28 days, 6-, 12 -, 18-, and 24-months post booster vaccination
Number of IFNγ Producing Cells/Million PBMCs
Applicable to the subset participants with additional blood collection. IFNγ producing cells as a measurement of cellular immunity will be assessed on a subset of the participants (40%) from each group. IFN-γ Enzyme-Linked ImmunoSpot (Elispot) assay will be performed on isolated peripheral blood mononuclear cells (PBMCs). Data will be reported as number of IFNγ producing cells/million and presented using means and 95% CI.
Measured: Baseline (pre-booster), 28 days, 6 and 12 months post booster vaccination
Frequency of Cytokine-expressing T Cells
Frequency of wild-type SARS-CoV-2 spike-specific cytokine-expressing T cells will be assessed in a subset of participants (~40%) using intracellular cytokine staining (ICS) by flow cytometry on PBMC samples. Results are reported as the frequency (%) of cytokine-expressing CD4 and CD8 memory T cells, summarised as geometric mean concentrations (GMCs) with 95% confidence intervals.
Measured: Baseline (pre-booster), 28 days, 6 and 12 months post-booster vaccination
Cellular Immunity: Multiplex Cytokine Assays - Reported as Cytokine Concentrations in pg/ml and Presented as GMC and 95% CI
Wild-type SARS-CoV-2 spike-specific cytokine concentrations following PBMC stimulation will be assessed in a predefined subset of participants (approximately 40%) using multiplex cytokine assays. Cytokine concentrations will be reported in pg/mL and summarised as geometric mean concentrations (GMCs) with 95% confidence intervals. IFN-γ ELISpot, intracellular cytokine staining (flow cytometry), and multiplex cytokine assays will be performed on isolated peripheral blood mononuclear cells (PBMCs).
Measured: Baseline (pre booster), 28 days-, 6 and 12 months post booster vaccination
Incidence of Unsolicited Adverse Events (AE)
All unsolicited AE will be collected for 28 days post booster vaccination. Data will be presented as proportion of participants who report unsolicited AE.
Measured: 28 days-post booster vaccination
Incidence of Medically Attended Adverse Events
All participants with medically attended AE will be collected for 3 months post booster vaccination. Data will be presented as number of participants who report unsolicited AE.
Measured: 3 months post booster vaccination
Incidence of Serious Adverse Events (SAE)
SAE will be collected throughout the follow-up period of 24 months post booster vaccination. Data will be presented as a proportion of participants who report unsolicited SAE.
Measured: 24 months post-booster
Incidence of PCR Confirmed COVID-19 Infection
Confirmed SARS-CoV-2 infections will be documented throughout the follow-up period, by clinical severity.
Measured: Up to 24 months post booster vaccination
Number of IFNγ Producing Cells/Million PBMCs
Applicable to the subset participants with additional blood collection. IFNγ producing cells as a measurement of cellular immunity will be assessed on a subset of the participants (40%) from each group. IFN-γ Enzyme-Linked ImmunoSpot (Elispot) assay will be performed on isolated peripheral blood mononuclear cells (PBMCs). Data will be reported as number of IFNγ producing cells/million and presented using means and 95% CI.
Measured: At 18 and 24 months post booster vaccination
Frequency of Cytokine-expressing T Cells
Frequency of wild-type SARS-CoV-2 spike-specific cytokine-expressing T cells will be assessed in a subset of participants (~40%) using intracellular cytokine staining (ICS) by flow cytometry on PBMC samples. Results are reported as the frequency (%) of cytokine-expressing CD4 and CD8 memory T cells, summarised as geometric mean concentrations (GMCs) with 95% confidence intervals.
Measured: 18 and 24 months post-booster vaccination
Cellular Immunity: Multiplex Cytokine Assays - Reported as Cytokine Concentrations in pg/ml and Presented as GMC and 95% CI
Wild-type SARS-CoV-2 spike-specific cytokine concentrations following PBMC stimulation will be assessed in a predefined subset of participants (approximately 40%) using multiplex cytokine assays. Cytokine concentrations will be reported in pg/mL and summarised as geometric mean concentrations (GMCs) with 95% confidence intervals. IFN-γ ELISpot, intracellular cytokine staining (flow cytometry), and multiplex cytokine assays will be performed on isolated peripheral blood mononuclear cells (PBMCs).
Measured: 18 and 24 months post booster vaccination

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

27 May 20226 Nov 2024

First posted3 Mar 2022
Study start27 May 2022
Primary completion30 Sep 2022
Study completion6 Nov 2024

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
Publications (4)Papers the sponsor has linked to this study.
Other trials for COVID-19Studies of the same condition, open and under way.
More trials run by Murdoch Childrens Research InstituteThe sponsor's other registered studies.
What the trial phases meanHow a treatment moves from first tests in people to approval.

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design

Study type: Interventional
Phase: Phase 3
Primary purpose: Prevention
Allocation: Randomised
Intervention model: Parallel groups
Model description: Study participants who have received two doses of either Sinopharm, AstraZeneca or Sputnik vaccine as their primary vaccine will be randomised into one of two groups. The two groups consist of a standard or fractional dose of Pfizer vaccine.
Masking: Quadruple blind
Who is masked: Participant, Care provider, Investigator, Outcomes assessor
Enrolment: 601 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT05265065
Sponsor's protocol ID: 81800
Status last verified: Mar 2026
First submitted: 1 Mar 2022
Last updated: 24 Mar 2026
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: Yes
FDA-regulated drug: Yes
FDA-regulated device: No
Individual data sharing: Yes: We will share de-identified data to ethically approved studies in cases where participants have indicated on the consent form that they consent to the use of their data and where consistent with terms of collaboration agreements.

Publications

Munro APS, Janani L, Cornelius V, Aley PK, Babbage G, Baxter D, Bula M, Cathie K, Chatterjee K, Dodd K, Enever Y, Gokani K, Goodman AL, Green CA, Harndahl L, Haughney J, Hicks A, van der Klaauw AA, Kwok J, Lambe T, Libri V, Llewelyn MJ, McGregor AC, Minassian AM, Moore P, Mughal M, Mujadidi YF, Murira J, Osanlou O, Osanlou R, Owens DR, Pacurar M, Palfreeman A, Pan D, Rampling T, Regan K, Saich S, Salkeld J, Saralaya D, Sharma S, Sheridan R, Sturdy A, Thomson EC, Todd S, Twelves C, Read RC, Charlton S, Hallis B, Ramsay M, Andrews N, Nguyen-Van-Tam JS, Snape MD, Liu X, Faust SN; COV-BOOST study group. Safety and immunogenicity of seven COVID-19 vaccines as a third dose (booster) following two doses of ChAdOx1 nCov-19 or BNT162b2 in the UK (COV-BOOST): a blinded, multicentre, randomised, controlled, phase 2 trial. Lancet. 2021 Dec 18;398(10318):2258-2276. doi: 10.1016/S0140-6736(21)02717-3. Epub 2021 Dec 2.
PubMed 34863358
Batmunkh T, Neal EF, Amraa O, Mazarakis N, Altangerel B, Avaa N, Batbayar L, Batsukh K, Bright K, Burentogtokh T, Do LAH, Dorj G, Hart JD, Jamiyandorj O, Javkhlantugs K, Jigjidsuren S, Justice F, Li S, Mashbaatar K, Moore KA, Namjil N, Nguyen CD, Ochirbat B, Surenjav U, Thomson H, Tsolmon B, Licciardi PV, von Mollendorf C, Mulholland K. Fractional BNT162b2 boosters induce durable immune responses after non-mRNA priming in Mongolia: a randomised controlled trial. Front Immunol. 2026 Mar 23;17:1789248. doi: 10.3389/fimmu.2026.1789248. eCollection 2026.
PubMed 41948336
Batmunkh T, Neal EFG, Amraa O, Mazarakis N, Altangerel B, Avaa N, Batbayar L, Batsukh K, Bright K, Burentogtokh T, Do LAH, Dorj G, Hart JD, Jamiyandorj O, Javkhlantugs K, Jigjidsuren S, Justice F, Li S, Mashbaatar K, Moore KA, Namjil N, Nguyen CD, Ochirbat B, Surenjav U, Thomson H, Tsolmon B, Licciardi PV, von Mollendorf C, Mulholland K. Immunogenicity and safety at twelve months of fractional and standard BNT162b2 booster doses in adults primed with ChAdOx1-S, BBIBP-CorV, or Gam-COVID-Vac in Mongolia: a randomised controlled trial. Vaccine. 2025 Nov 14;66:127840. doi: 10.1016/j.vaccine.2025.127840. Epub 2025 Oct 9.
PubMed 41072276
Batmunkh T, Moore KA, Thomson H, Altangerel B, Amraa O, Avaa N, Batbayar L, Batsukh K, Bright K, Burentogtokh T, Ha Do LA, Dorj G, Hart JD, Javkhlantugs K, Jigjidsuren S, Justice F, Li S, Licciardi PV, Mashbaatar K, Mazarakis N, Neal EFG, Nguyen CD, Ochirbat B, Tsolmon B, Tuya A, Surenjav U, von Mollendorf C, Mulholland K. Immunogenicity, safety, and reactogenicity of a half- versus full-dose BNT162b2 (Pfizer-BioNTech) booster following a two-dose ChAdOx1 nCoV-19, BBIBP-CorV, or Gam-COVID-Vac priming schedule in Mongolia: a randomised, controlled, non-inferiority trial. Lancet Reg Health West Pac. 2023 Nov 21;42:100953. doi: 10.1016/j.lanwpc.2023.100953. eCollection 2024 Jan.
PubMed 38357398

Want to know more?

The sponsor has not listed a contact. The official record may have more details.

Talk to your doctor first and take this page with you. Only the study team can confirm whether you can join.

Questions to ask the study team

What is the study trying to find out?
What would I need to do, and how often would I visit?
Could I receive a placebo instead of the treatment?
What are the possible risks and benefits for me?
Will it cost me anything? Are travel or time paid for?
Can I keep seeing my own doctor during the study?
What happens when the study ends?

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Study at a glance

From the registry record, last updated by the sponsor on 24 Mar 2026. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: A Randomised Controlled Trial to Assess the Immunogenicity, Safety and Reactogenicity of Standard Dose Versus Fractional Doses of COVID-19 Vaccine (Pfizer-BioNTech) Given as a Booster Dose After Priming With Sinopharm, AstraZeneca or Sputnik in Healthy Adults in Mongolia
ClinicalTrials.gov ID: NCT05265065
Acronym / sponsor ID: 81800
Conditions: COVID-19
Keywords: Booster dose, Pfizer, fractional and standard doses, COVID-19 vaccination, mRNA vaccine
Phase: Phase 3
Study type: Interventional
Recruitment status: Completed
Enrolment: 601 participants (actual)
Lead sponsor: Murdoch Childrens Research InstituteUniversity, hospital or other
Collaborators: Coalition for Epidemic Preparedness Innovations, The Peter Doherty Institute for Infection and Immunity
Study start: 27 May 2022 (actual)
Primary completion: 30 Sep 2022 (actual)
Study completion: 6 Nov 2024 (actual)
First posted: 3 Mar 2022 (actual)
Results: Posted 19 Sep 2024

Clinical summary

The research question as the sponsor registered it. This describes what the study plans to test, not what it found.

Detailed description

As per brief summary

Study design

Primary purpose: Prevention
Allocation: Randomised
Intervention model: Parallel groups
Masking: Quadruple blind (participant, care provider, investigator, outcomes assessor)
Number of arms: 2
Model description: Study participants who have received two doses of either Sinopharm, AstraZeneca or Sputnik vaccine as their primary vaccine will be randomised into one of two groups. The two groups consist of a standard or fractional dose of Pfizer vaccine.

Arm	Type	Receives
Standard Pfizer-BioNTech booster group	Active comparator	Biological: Tozinameran - Standard DoseBiological/Vaccine: Tozinameran - Standard Dose Other Names: BNT162b2 Comirnaty Pfizer Covid-19 vaccine Tozinameran is a single-stranded, 5'-capped messenger RNA (mRNA) produced using a cellfree in vitro transcription from the corresponding DNA templates, encoding the viral spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Dose - 30 µg in 0.3 ml. Liquid for injection. Single dose.
Fractional Pfizer-BioNTech booster group	Experimental	Biological: Tozinameran - Fractional DoseBiological/Vaccine: Tozinameran - Standard Dose Other Names: BNT162b2 Comirnaty Pfizer Covid-19 vaccine Tozinameran is a single-stranded, 5'-capped messenger RNA (mRNA) produced using a cellfree in vitro transcription from the corresponding DNA templates, encoding the viral spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Dose - 15 µg in 0.3 ml. Liquid for injection. Single dose.

Who may qualify

Ages: 18 years and older
Sex: All
Healthy volunteers: Accepted
Age groups: Adult, Older adult

Key inclusion criteria (4 listed)

Have completed two doses of Sinopharm, AstraZeneca or Sputnik vaccines with the recommended schedule 6 months prior to the date of enrolment
Willing and able to give written informed consent
Aged 18 years or above
Willing to complete the follow-up requirements of the study

Key exclusion criteria (8 listed)

Received 3 doses of COVID-19 vaccine
Received 2 doses of COVID-19 less than 6 months prior to the start of the trial
Currently on immunosuppressive medication or anti-cancer chemotherapy
HIV infection
Congenital immune deficiency syndrome

Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.

Interventions

Intervention	Type	Arms
Tozinameran - Standard DoseAlso: BNT162b2, Comirnaty, Pfizer Covid-19 vaccineTozinameran is a single-stranded, 5'-capped messenger RNA (mRNA) produced using a cellfree in vitro transcription from the corresponding DNA templates, encoding the viral spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Dose - 30 µg in 0.3 ml. Liquid for injection. Single dose.	Biological	Standard Pfizer-BioNTech booster group
Tozinameran - Fractional DoseAlso: BNT162b2, Comirnaty, Pfizer Covid-19 vaccineTozinameran is a single-stranded, 5'-capped messenger RNA (mRNA) produced using a cellfree in vitro transcription from the corresponding DNA templates, encoding the viral spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Dose - 15 µg in 0.15 ml. Liquid for injection. Single dose.	Biological	Fractional Pfizer-BioNTech booster group

Primary outcome

Seroresponse
Time frame: 28-days post booster vaccination
Serum samples collected at 28-days post booster vaccination from all groups will be evaluated for SARS-CoV-2 specific IgG antibodies using IgG ELISA. The primary endpoint is the seroresponse rate at the Day-28 visit. The seroresponse rate at the individual level is defined as either a ≥4-fold rise in binding antibodies at the Day-28 visit compared to baseline (pre-vaccination) with a titre of <200 BAU/ml, a ≥2-fold rise among participants with a baseline (pre-vaccination) titre of >200 BAU/ml, or a ≥4-times the lower limit of detection if baseline levels are lower than the limit of detection.
Solicited Grade 3 or 4 Local or Systemic Reaction
Time frame: 7 days post booster vaccination
Questionnaire to document solicited reactions is developed specifically for this study. Data will be reported as the proportion of participants who report grade 3 or 4 reactions by each intervention arm. Solicited reactions such as pain, tenderness, erythema/redness, induration, swelling, fever, nausea, vomiting, headache, fatigue/malaise, myalgia, arthralgia, diarrhea, enlarged lymph nodes will be collected from the participants 7 days post-vaccination.

17 secondary outcomes

Seroresponse by Priming Vaccine Strata
Time frame: 28-days post booster vaccination
SARS-CoV-2 Specific IgG Antibodies at Day-28
Time frame: 28-days post booster vaccination
SARS-CoV-2 Specific IgG Antibodies at Day-28 by Priming Vaccine Strata
Time frame: 28-days post booster vaccination
SARS-CoV-2 Specific IgG Antibodies at Baseline (Pre-booster), 28 Days, 6 Months, 12 Months, 18 Months, and 24 Months Post-booster Vaccination.
Time frame: Baseline (pre booster), 28 days, 6 months, 12 months, 18 months, and 24 months post-booster vaccination.
SARS-CoV-2 Specific Neutralising Antibodies at Baseline (Pre-booster), 28 Days, 6 Months, 12 Months, 18 Months, and 24 Months Post-booster Vaccination Measured by Surrogate Virus Neutralisation Test (sVNT).
Time frame: Baseline (pre-booster), 28 days, 6 months, 12 months, 18 months, and 24 months post-booster vaccination.
SARS-CoV-2 Specific Neutralising Antibodies at Baseline (Pre Booster), 28 Days-, 6- and 12-months Post Booster Vaccination Measured by SARS-CoV-2 Microneutralisation Assay
Time frame: Baseline (pre booster), 28 days-, 6- and 12-months post booster vaccination
Interferon Gamma (IFNγ) Concentrations in International Units (IU)/mL
Time frame: Baseline (pre booster), 28 days, 6-, 12 -, 18-, and 24-months post booster vaccination
Number of IFNγ Producing Cells/Million PBMCs
Time frame: Baseline (pre-booster), 28 days, 6 and 12 months post booster vaccination
Frequency of Cytokine-expressing T Cells
Time frame: Baseline (pre-booster), 28 days, 6 and 12 months post-booster vaccination
Cellular Immunity: Multiplex Cytokine Assays - Reported as Cytokine Concentrations in pg/ml and Presented as GMC and 95% CI
Time frame: Baseline (pre booster), 28 days-, 6 and 12 months post booster vaccination
Incidence of Unsolicited Adverse Events (AE)
Time frame: 28 days-post booster vaccination
Incidence of Medically Attended Adverse Events
Time frame: 3 months post booster vaccination
Incidence of Serious Adverse Events (SAE)
Time frame: 24 months post-booster
Incidence of PCR Confirmed COVID-19 Infection
Time frame: Up to 24 months post booster vaccination
Number of IFNγ Producing Cells/Million PBMCs
Time frame: At 18 and 24 months post booster vaccination
Frequency of Cytokine-expressing T Cells
Time frame: 18 and 24 months post-booster vaccination
Cellular Immunity: Multiplex Cytokine Assays - Reported as Cytokine Concentrations in pg/ml and Presented as GMC and 95% CI
Time frame: 18 and 24 months post booster vaccination

Results and safety

Results posted to the registry on 19 Sep 2024, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
Standard	300	282
Fractional	301	285

Primary outcome: Seroresponse

Time frame: 28-days post booster vaccination. Count of participants. Unit: Participants

Measure	Standard n = 292	Fractional n = 295
Value	253	250

Standard vs Fractional: Risk Difference (RD): -2.9 (95% CI -7.7 to 2.0), Regression, Logistic

Population analysed: The analysis of immunogenicity endpoints included all participants with outcome data. There are two study arms, as per "Arms and Interventions" in Protocol Section, corresponding to the primary analysis comparing a full dose to a fractional dose. Stratified randomisation was performed to ensure balanced randomisation according to the primary vaccine received (prior to this study) and age for secondary subgroup analyses. The primary outcome is unstratified.

Primary outcome: Solicited Grade 3 or 4 Local or Systemic Reaction

Time frame: 7 days post booster vaccination. Count of participants. Unit: Participants

Measure	Standard n = 299	Fractional n = 299
Value	6	4

Population analysed: The reactogenicity and safety analysis populations included all randomised participants who received a study vaccine, according to the vaccine received. There are two study arms, as per "Arms and Interventions" in Protocol Section. Stratified randomisation was performed to ensure balanced randomisation according to the primary vaccine received (prior to this study) and age for secondary subgroup analyses. The primary outcome is unstratified.

17 secondary outcomes are reported in the full results.

Adverse events

Time frame: Solicited local and systemic adverse events (AEs) were collected from the participants 7 days post-vaccination Unsolicited AEs up to 28 days following vaccination observed by the Investigator or reported by the participant, whether or not attributed to study medication, were also collected. Serious adverse events (SAE's) will be followed up for the duration of the trial up to 24 months.. Other adverse events reported at 0% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
Standard Pfizer-BioNTech Booster Group- AstraZeneca	0 of 65 (0%)	5 of 65 (7.7%)	0 of 65
Fractional Pfizer-BioNTech Booster Group- AstraZeneca	2 of 65 (3.1%)	7 of 65 (10.8%)	0 of 65
Standard Pfizer-BioNTech Booster Group- Sinopharm	2 of 201 (1%)	10 of 201 (5%)	0 of 201
Fractional Pfizer-BioNTech Booster Group- Sinopharm	0 of 200 (0%)	7 of 200 (3.5%)	0 of 200
Standard Pfizer-BioNTech Booster Group- Sputnik	1 of 34 (2.9%)	5 of 34 (14.7%)	0 of 34
Fractional Pfizer-BioNTech Booster Group- Sputnik	0 of 36 (0%)	5 of 36 (13.9%)	0 of 36

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 24 Mar 2026.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Background: PubMed 34863358Munro APS, Janani L, Cornelius V, Aley PK, Babbage G, Baxter D, Bula M, Cathie K, Chatterjee K, Dodd K, Enever Y, Gokani K, Goodman AL, Green CA, Harndahl L, Haughney J, Hicks A, van der Klaauw AA, Kwok J, Lambe T, Libri V, Llewelyn MJ, McGregor AC, Minassian AM, Moore P, Mughal M, Mujadidi YF, Murira J, Osanlou O, Osanlou R, Owens DR, Pacurar M, Palfreeman A, Pan D, Rampling T, Regan K, Saich S, Salkeld J, Saralaya D, Sharma S, Sheridan R, Sturdy A, Thomson EC, Todd S, Twelves C, Read RC, Charlton S, Hallis B, Ramsay M, Andrews N, Nguyen-Van-Tam JS, Snape MD, Liu X, Faust SN; COV-BOOST study group. Safety and immunogenicity of seven COVID-19 vaccines as a third dose (booster) following two doses of ChAdOx1 nCov-19 or BNT162b2 in the UK (COV-BOOST): a blinded, multicentre, randomised, controlled, phase 2 trial. Lancet. 2021 Dec 18;398(10318):2258-2276. doi: 10.1016/S0140-6736(21)02717-3. Epub 2021 Dec 2.
Derived from this study: PubMed 41948336Batmunkh T, Neal EF, Amraa O, Mazarakis N, Altangerel B, Avaa N, Batbayar L, Batsukh K, Bright K, Burentogtokh T, Do LAH, Dorj G, Hart JD, Jamiyandorj O, Javkhlantugs K, Jigjidsuren S, Justice F, Li S, Mashbaatar K, Moore KA, Namjil N, Nguyen CD, Ochirbat B, Surenjav U, Thomson H, Tsolmon B, Licciardi PV, von Mollendorf C, Mulholland K. Fractional BNT162b2 boosters induce durable immune responses after non-mRNA priming in Mongolia: a randomised controlled trial. Front Immunol. 2026 Mar 23;17:1789248. doi: 10.3389/fimmu.2026.1789248. eCollection 2026.
Derived from this study: PubMed 41072276Batmunkh T, Neal EFG, Amraa O, Mazarakis N, Altangerel B, Avaa N, Batbayar L, Batsukh K, Bright K, Burentogtokh T, Do LAH, Dorj G, Hart JD, Jamiyandorj O, Javkhlantugs K, Jigjidsuren S, Justice F, Li S, Mashbaatar K, Moore KA, Namjil N, Nguyen CD, Ochirbat B, Surenjav U, Thomson H, Tsolmon B, Licciardi PV, von Mollendorf C, Mulholland K. Immunogenicity and safety at twelve months of fractional and standard BNT162b2 booster doses in adults primed with ChAdOx1-S, BBIBP-CorV, or Gam-COVID-Vac in Mongolia: a randomised controlled trial. Vaccine. 2025 Nov 14;66:127840. doi: 10.1016/j.vaccine.2025.127840. Epub 2025 Oct 9.
Derived from this study: PubMed 38357398Batmunkh T, Moore KA, Thomson H, Altangerel B, Amraa O, Avaa N, Batbayar L, Batsukh K, Bright K, Burentogtokh T, Ha Do LA, Dorj G, Hart JD, Javkhlantugs K, Jigjidsuren S, Justice F, Li S, Licciardi PV, Mashbaatar K, Mazarakis N, Neal EFG, Nguyen CD, Ochirbat B, Tsolmon B, Tuya A, Surenjav U, von Mollendorf C, Mulholland K. Immunogenicity, safety, and reactogenicity of a half- versus full-dose BNT162b2 (Pfizer-BioNTech) booster following a two-dose ChAdOx1 nCoV-19, BBIBP-CorV, or Gam-COVID-Vac priming schedule in Mongolia: a randomised, controlled, non-inferiority trial. Lancet Reg Health West Pac. 2023 Nov 21;42:100953. doi: 10.1016/j.lanwpc.2023.100953. eCollection 2024 Jan.
Quarter-dose of Moderna COVID vaccine still rouses a big immune responseLink provided by the sponsor.
US Food and Drug Administration (FDA). Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventive Vaccine Clinical Trials 2007Link provided by the sponsor.
Australian Technical Advisory Group on Immunisation (ATAGI). ATAGI recommendations on the use of a booster dose of COVID-19 vaccine 2021Link provided by the sponsor.
Individual participant dataSharing planned: Yes. We will share de-identified data to ethically approved studies in cases where participants have indicated on the consent form that they consent to the use of their data and where consistent with terms of collaboration agreements.

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Referral and contact

AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.

Tsetsegsaikhan Batmunkh, MD principal investigator

Ministry of Health, Mongolia

Kim Mulholland, MD/Prof principal investigator

Murdoch Childrens Research Institute

1 site in 1 country: see every site and its status.

Questions about this trial

What is this clinical trial studying?

A Phase 3 study testing Tozinameran - Standard Dose and Tozinameran - Fractional Dose in people with COVID-19, run by Murdoch Childrens Research Institute at 1 site in Mongolia.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 4 inclusion and 8 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: finished, as of the sponsor's last update on 24 Mar 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 1 site in Mongolia. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

Yes. Results are posted in the registry (first posted 19 Sep 2024). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Seroresponse (time frame: 28-days post booster vaccination). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT05265065, which also lists 4 linked publications.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 24 Mar 2026.