A Phase 4 interventional study of BNT162b2 in COVID 19 Vaccine, sponsored by The University of Hong Kong. Completed at 1 site in Hong Kong. Open to participants aged 30 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-05-15.
Sponsored by The University of Hong Kong · Phase 4, Interventional, and Prevention
300 adults ≥30 years of age who have previously received two doses of an inactivated COVID-19 vaccine at least 3 months earlier will receive a third dose with an mRNA vaccine (BNT162b2, BioNTech). Investigators will monitor reactogenicity and measure the immune response to the third dose.
Background: The accrual of population immunity to COVID-19 could allow life to return to pre- pandemic normality. Immunity can be acquired through natural infections or, preferably, by vaccination. An unprecedented global effort has succeeded in developing a number of COVID-19 vaccines. All vaccines against COVID-19 approved until now have originally been developed as either a single dose or following a homologous two-dose regimen. Inactivated COVID-19 vaccines have shown inferior immunogenicity compared to mRNA vaccines but there are no studies looking into the immunogenicity, reactogenicity and safety profile of mRNA vaccination provided as a booster dose in individuals who have previously received two doses of an inactivated COVID-19 vaccine.
Aims and Objectives: The aims of this study are: (1) to determine whether one dose of mRNA vaccine can boost neutralizing antibodies against SARS-CoV-2 in individuals who have previously received two doses of inactivated COVID-19 vaccines, and (2) to assess the reactogenicity and safety of heterologous 3rd doses of vaccination. The specific primary objective of this study is to assess the vaccine (humoral) immunogenicity, proxy by SARS-CoV-2 serum neutralizing antibody titers, of a 3rd dose dose of mRNA vaccine (using BNT162b2, Fosun/BioNTech) at 28 days after the booster dose in individuals who have previously received two doses of any inactivated COVID-19 vaccines.
Study design: Open label trial in adults aged 30 years of age or older (at enrolment). The duration of participation for each participant will be 12 months from the administration of the 3rd vaccine dose. The immune response and reactogenicity of one dose of BNT162b2 will be investigated in individuals who previously received two doses of any inactivated COVID-19 vaccines at least 3 months earlier. Participants will be enrolled shortly before receiving the booster dose of BNT162b2 (day 0), with blood collection at days 0, 28, 182 and 365 days after enrolment for analysis of humoral immune responses.
Main outcomes: The primary outcome is the vaccine immunogenicity measured as SARS-CoV-2 serum neutralizing antibodies in individuals who previously received two doses of any inactivated COVID-19 vaccines, evaluated as the geometric mean titer (GMT) at 28 days after the 3rd dose. The secondary outcomes include (1) a comparison of SARS- CoV-2 serum neutralizing antibodies as the geometric mean fold rise from baseline to each post-vaccination timepoint (i.e. at days 28, 182 and 365), and (2) descriptive analysis of the reactogenicity and safety profile of the 3rd dose.
Target population: Adults aged 30 years or older
Number of Subjects Planned: 300 participants to be recruited between September 2021 and December 2021
Study duration: 12 months for each participant
Potential implications: This study will provide important evidence into the effects of using a 3rd dose of mRNA vaccines to boost the immune response in individuals that had previously received two doses of inactivated vaccines. This information together with data collected on reactogenicity and safety could inform COVID-19 vaccination policy locally and internationally.
The University of Hong Kong is the lead sponsor of 1,262 studies on the registry; 340 are open to participants now.
Of its 8 completed or terminated interventional studies of FDA-regulated products, 0 (0%) have results posted.
Counted across the registry records on this site, refreshed daily.
Exclusion Criteria:
BNT162b2 mRNA vaccine (Cominarty®, BioNTech/Fosun Pharma), one dose (0.3mL after dilution) contains 30 micrograms of COVID-19 mRNA Vaccine embedded in lipid nanoparticles.
Biological: BNT162b2
BNT162b2 mRNA vaccine (Cominarty®, BioNTech/Fosun Pharma), one dose (0.3mL after dilution) contains 30 micrograms of COVID-19 mRNA Vaccine embedded in lipid nanoparticles.
Also known as: Comirnaty
Geometric Mean Titer of SARS-CoV-2 serum neutralizing antibodies
The primary outcome measure is the vaccine (humoral) immunogenicity at 28 days after the booster dose of BNT162b2 in individuals who have previously received two doses of any inactivated COVID-19 vaccines, measured as geometric mean titer (GMT) of SARS-CoV-2 serum neutralizing antibodies using plaque reduction neutralization test (PRNT).
Time frame: 28 days after vaccination
Geometric Mean Titer of SARS-CoV-2 serum neutralizing antibodies
Time frame: 182 and 365 days after vaccination
The geometric mean fold rise (GMFR) of SARS-CoV-2 serum neutralizing antibody titers from baseline to each post-vaccination timepoint measured.
Time frame: Day 28, 49, 182 and 365 after vaccination
Reactogenicity
Incidence of solicited local and systemic adverse events after the booster dose of vaccination.
Time frame: 7 days after vaccination or until the last symptom disappears
Hospitalizations from any cause
Incidence of hospitalizations during the year after receipt of the booster dose.
Time frame: 365 days after vaccination
Plan to share: Yes
This study is completed, as verified in Apr 2026. You cannot join it, but the record below documents what was studied.
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The University of Hong Kong