Immunogenicity and Safety of Fractional Booster Dose of COVID-19 Vaccines Available for Use in Pakistan/Brazil: A Phase 4 Dose-optimizing Trial

  • End date
    Jun 11, 2023
  • participants needed
  • sponsor
    Albert B. Sabin Vaccine Institute
Updated on 11 August 2022
Accepts healthy volunteers


Since the emergence of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pathogen in late 2019, millions of people around the world have fallen ill and died from coronavirus disease 2019 (COVID-19), with variant-fueled case spikes causing repeated cycles of morbidity and mortality. The rapid development and emergency use authorization of vaccines against SARS-CoV-2 presents an enormous opportunity to protect populations, but bottlenecks in production have led to demand for vaccines that far outpaces supply. This project will investigate the immunogenicity of fractional doses of SARS-CoV-2 vaccines given a minimum of six months following an initial two-dose schedule or following natural immunity via documented infection. The consortium of research partners from the Sabin Vaccine Institute, Aga Khan University, Fundação Oswaldo Cruz (Fiocruz), and Stanford University will recruit volunteers to receive a full or fractional booster dose of BNT162b2, AZD1222 or Sinovac following receipt of their primary vaccination series or PCR-confirmed natural infection in Pakistan. The research team will follow participants for six months from boosting, with blood draws at baseline, 28 days, 3 months and 6 months, and measure sero-response rate (SRR) by anti-Spike immunoglobulin G (IgG) binding enzyme-linked immunosorbent assay (ELISA) with the ultimate aim of identifying whether fractional doses provide a similar immune response compared to full doses of vaccine.

Condition COVID-19
Treatment BNT162b2, AZD1222, Sinovac
Clinical Study IdentifierNCT05343871
SponsorAlbert B. Sabin Vaccine Institute
Last Modified on11 August 2022


Yes No Not Sure

Inclusion Criteria

Healthy male or female individuals aged 18 years to 60 years
Participant is willing and able to give written informed consent for participation in the trial
Individuals who can comply with trial procedures and are available for the duration of follow-up
● Previous vaccination with a complete primary series of Sinovac (Priming Group 1), AZD1222
(Priming Group 2), or BNT162b2 (Priming Group 3-B) at least 6 months prior to screening
● Previous vaccination with a complete primary series of Sinovac (Priming Group 1) or
AZD1222 (Priming Group 2) at least 6 months prior to screening, or PCR-confirmed natural
infection (Priming Group 3-P) between February 2021 - 6 months prior to screening

Exclusion Criteria

Has a contraindication to BNT162b2, AZD1222 or Sinovac
Has received an incomplete primary COVID-19 vaccination series
Has received 3 doses of COVID-19 vaccine
Has received heterologous primary COVID-19 vaccination series
History of a solid organ or bone marrow transplant
History of malignancy (other than non-melanoma skin cancer) within the past five years
Currently on hemodialysis
Any confirmed or suspected immunosuppressive or immunodeficiency condition or
On chronic (>30 days) use of immunosuppressive medications at the time of enrollment
(except topical steroids or short-term oral steroids, i.e., ≤14 days)
Known diagnosis of HIV with CD4 count <200 cells/mm3 (in the past 6 months)
Active or history of previous auto-immune neurological disorders (e.g., multiple
sclerosis, Guillain-Barre syndrome, transverse myelitis) (excluding Bell's palsy)
Has received anti-CD20 monoclonal antibodies for any reason in the past 12 months
Has received monoclonal antibodies to treat a previous COVID-19 event
Pregnant at screening
Positive SARS-CoV-2 Antigen test in respiratory specimen at screening
Planning to migrate out of the study area within 6 months of the enrollment
Participants currently enrolled in any other COVID-19 vaccine research trial in which
they are getting a COVID-19 vaccine during the study period
Illiterate individuals (Brazil only)
Has a severe and/or uncontrolled comorbidity
Pakistan (natural infection Priming Group (Priming Group 3-P))
● Prior vaccination with ANY vaccine against COVID-19
Clear my responses

How to participate?

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Additional screening procedures may be conducted by the study team before you can be confirmed eligible to participate.

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If you are confirmed eligible after full screening, you will be required to understand and sign the informed consent if you decide to enroll in the study. Once enrolled you may be asked to make scheduled visits over a period of time.

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Complete your scheduled study participation activities and then you are done. You may receive summary of study results if provided by the sponsor.

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