Third Dose Vaccination With AstraZeneca or Pfizer COVID-19 Vaccine Among Adults Received Sinovac COVID-19 Vaccine

A Randomized, Observer-blind Trial to Assess the Immunogenicity and Safety of Third Dose Vaccination With AstraZeneca COVID-19 Vaccine or Pfizer/BioNTech COVID-19 Vaccine Among Thai Adults Receiving Two Doses of Sinovac

Status

Completed

Phases

Phase 2

Study type

Interventional

Source

ClinicalTrials.gov

Registry ID

NCT05049226

Enrollment

1250

Registered

2021-09-20

Start date

2021-09-24

Completion date

2022-02-22

Last updated

2022-07-06

For informational purposes only — not medical advice. Sourced from public registries and may not reflect the latest updates. Terms

Conditions

COVID-19 Infection, COVID-19 VACCINE

Keywords

COVID-19 Infection, COVID-19 Respiratory Infection, COVID-19 VACCINE, AstraZeneca COVID-19 VACCINE, AstraZeneca COVID-19 (ChAdOx1 AZD1222) vaccine, Pfizer/BioNTech COVID-19 VACCINE, Pfizer/BioNTech COVID-19 (BNT162b2) vaccine, Thai adults, full dose AstraZeneca COVID-19 VACCINE, half dose AstraZeneca COVID-19 VACCINE, full dose Pfizer/BioNTech COVID-19 VACCINE, half dose Pfizer/BioNTech COVID-19 VACCINE, Sinovac COVID-19 Vaccine, immunogenicity, safety

Brief summary

This prospective, multi-center, randomized, observer-blind Phase 2 study. A total of 1320 participants will be divided into 2 groups (660 each) receiving either full dose or half dose of either AZ or PF. Each group is further stratified into 3 subgroups according to three interval duration in term of days after second dose of SV for 60 to less than 90 days, 90 to less than120 days and 120 to 180 days. Each group will be randomized to receive either AZ or PF in 1:1 ratio. Subjects who fulfilled eligibility criteria will be randomly assigned to receive either full dose or half dose of AZ or PF in 1:1 ratio as an IM injection in the deltoid muscle at Visit 1 (V1). Subjects will be follow-up for assessing immunity at day 28 (V3), day 60 (V4) and day 90 (V5) and for safety at day 7 (V2), day 28 (V3), day 60 (V4) and day 90 (V5). At least 50% from each subgroup will be randomly selected to provide additional blood at baseline (V1, day 0) and day 28 (V3) to be used for assessment of T-cell-mediated immunity (CMI)

Detailed description

This study has been designed to assess immune response and safety of third dose vaccination with AstraZeneca ChAdOx1AZD1222 vaccine or Pfizer/BioNTech BNT162b2 vaccine among Thai subjects who have received two doses of Sinovac. The types of vaccines provided by the government included 7.7 million doses of inactivated vaccine manufactured by Sinovac and 6.5 million doses of AstraZeneca ChAdOx1 AZD1222 vaccine. With the limited supplies of COVID vaccines in many regions of the world especially in LMIC including Thailand and the evidences of waning immunity of especially inactivated vaccine have raised the concerns whether third dose is needed. The third dose that available now in Thailand are AstraZeneca ChAdOx1AZD1222 vaccine (AZ)/ Pfizer/BioNTech BNT162b2 vaccine (PF) and whether this can be provided with half dose so that the vaccination coverage is going to be higher in spite of limited vaccine supplies. A number of studies have proved that COVID-19 vaccines are effective at preventing people from getting severe COVID-19 disease. However, the vaccines do not only reduce the chance of infection, but they also help to mitigate disease severity. Study population: Male and female adults aged equal or more than 20 years who received two doses of Inactivated COVID-19 vaccine developed by Sinovac (given at 21-28 days apart) at different intervals of 60 to less than 90 days, 90 to less than120 days and 120 to 180 days This prospective, multi-center, randomized, observer-blind Phase 2 study, A total of 1320 participants will be divided into 2 groups (660 each) receiving either full dose or half dose of either AZ or PF. Each group is further stratified into 3 subgroups according to three interval duration in term of days after second dose of SV for 60-less than 90 days, 90-less than120 days and 120-180 days respectively. Subjects who fulfilled eligibility criteria will be randomly assigned to receive either full dose or half dose of AZ or PF in 1:1 ratio as an IM injection in the deltoid muscle at Visit 1 (V1). All participants will be randomized based on dose given either full dose or half dose and further stratify accordingly by Interactive web-based response system (IWRS). There will be unblinded team which consists of pharmacist and nurse who will give injection. All the safety assessment will be performed independently by clinical team. Subjects will be follow-up for assessing immunity at day 28 (V3), day 60 (V4) and day 90 (V5) and for safety at day 7 (V2), day 28 (V3), day 60 (V4) and day 90 (V5).

Interventions

BIOLOGICALAstraZeneca ChAdOx1 AZD1222 vaccine (AZ) full dose

Astrazeneca COVID-19 (ChAdOx1 AZD1222) vaccine: One dose (0.5 ml) contains: COVID-19 Vaccine (ChAdOx1-S\* recombinant) 5 × 10\^10 viral particles (vp) \*Recombinant, replication-deficient chimpanzee adenovirus vector encoding the SARS-CoV-2 Spike glycoprotein. Produced in genetically modified human embryonic kidney (HEK) 293 cells. Administer: Intramuscular (IM) injection in the deltoid muscle

BIOLOGICALPfizer/BioNTech BNT162b2 vaccine (PF) full dose

Pfizer-BioNTech COVID-19 (BNT162b2) vaccine: Diluent: 0.9% sodium chloride (normal saline, preservative-free) Administer: Intramuscular (IM) injection in the deltoid muscle

BIOLOGICALAstraZeneca ChAdOx1 AZD1222 vaccine (AZ) half dose

BIOLOGICALPfizer/BioNTech BNT162b2 vaccine (PF) half dose

Pfizer-BioNTech COVID-19 (BNT162b2) vaccine: Diluent: 0.9% sodium chloride (normal saline, preservative-free) Administer: Intramuscular (IM) injection in the deltoid muscle

Study design

Allocation

RANDOMIZED

Intervention model

PARALLEL

Primary purpose

PREVENTION

Masking

DOUBLE (Subject, Investigator)

Masking description

Unblinded study staff will be responsible for preparing study products (in accordance with the randomly determined assignment), administering the study vaccine, and handling all drug accountability procedures. These personnel will not participate in the other aspects of the clinical trial, to help ensure the integrity of the blind at the site. Unblinded staff will retrieve a participant's randomization assignment after being informed by the PI or designee that a participant is eligible for randomization. They will prepare study vaccine (AZ or PF) with dose (full or half dose) based on the participant's randomization

Eligibility

Sex/Gender

ALL

Age

20 Years to No maximum

Healthy volunteers

Yes

Inclusion criteria

1. Adult male or female age equal or more than 20 years with Thai ID cards 2. Received two doses (21-28 days apart) of Sinovac inactivated COVID-19 vaccine who will be divided according to their intervals 60-less than 90 days, 90-less than120 days and 120-180 days 3. Has provided written informed consent prior to performance of any study-specific procedure 4. No history of fever or PUI symptoms within 7 days

Exclusion criteria

1. Any confirmed or suspected immunosuppressive or immunodeficient state. 2. Contraindication to AZ or PF according to labelling of the products 3. History of COVID infection within 3 months period 4. Pregnancy

Design outcomes

Primary

Measure	Time frame	Description
Frequency of SAEs	Day 0 through Day 90	Frequency and percentage of SAEs throughout the entire study period
GMFR changed from baseline in anti-S IgG GMT after vaccination	Day 28, Day 60 and Day 90	GMFR changed from baseline in anti-S IgG GMT at 28,60 and 90 days after vaccination
Anti-S IgG Seroresponses changed from baseline after vaccination	Day 28, Day 60 and Day 90	Frequency and percentage of participants with seroresponses in anti-S IgG titer as defined by (1) a ≥ 4-fold increase from baseline at 28, 60 and 90 days after vaccination (2) a ≥ 10-fold increase from baseline at 28,60 and 90 days after vaccination
GMT against SARS-Cov-2 pseudovirus (PVNT) Neutralizing antibody titer 50 at baseline and after vaccination	Day 0, Day 28 and Day 90	GMT against SARS-Cov-2 pseudovirus (PVNT) Neutralizing antibody titer 50 at baseline and after vaccination at day 28 and day 90
GMFR changed from baseline in NT50 against SARS-CoV-2 pseudovirus after vaccination	Day 28 and Day 90	GMFR changed from baseline in NT50 against SARS-CoV-2 pseudovirus at 28 and 90 days vaccination
Frequency of solicited reportable local adverse event after vaccination	Day 0 through Day 7	Frequency and percentage of solicited reportable local adverse events (pain or tenderness, erythema, swelling or induration) of vaccination
Frequency of solicited reportable systemic adverse event after vaccination	Day 0 through Day 7	Frequency and percentage of solicited reportable systemic adverse events (fever, headache, fatigue or malaise, myalgia, arthralgia, nausea or vomitting) of vaccination
Frequency of all unsolicited AEs	Day 0 through Day 28	Frequency and percentage of all unsolicited AEs
GMT Anti-S IgG at baseline and after vaccination	Day 0, Day 28, Day 60 and Day 90	GMT Anti-S IgG at baseline and after vaccination at day 28, day 60 and day 90

Secondary

Measure	Time frame	Description
NT50 GMT against SARS-Cov-2 by micro neutralization assay at baseline and day 28 and day 90 after vaccination	Day 0, Day 28 and Day 90	NT50 GMT against SARS-Cov-2 by micro neutralization assay at baseline and day 28 and 90 after vaccination
GMFR changed from baseline in NT50 against SARS-CoV-2 (micro NT Delta/WT NA) at 28 and 90 days after vaccination among those positives by PNT assay	Day 28 and Day 90	GMFR changed from baseline in NT50 against SARS-CoV-2 (micro NT Delta/WT NA) at 28 and 90 days after vaccination among those positives by PNT assay
NT50 seroresponses against SARS-CoV-2 using micro NT changed from baseline at 28 and 90 days after vaccination among those positive by PVNT assay	Day 28 and Day 90	Frequency and percentage of participants with NT50 seroresponses against SARS-CoV-2 using micro NT as defined by (1) a ≥ 4-fold increase from baseline at 28 and 90 days after vaccination compare to baseline among those positive by PVNT assay

Other

Measure	Time frame	Description
Seroresponse against SARS-CoV-2 pseudovirus towards Omicron strains at baseline, 28 and 90 days after vaccination	Day 0, 28 and 90	Frequency and percentage of subjects with % inhibition response at 1:80 dilution against SARS-CoV-2 pseudovirus as defined by more than 50% and 68% inhibition towards Omicron strains
S protein-specific T cells response at baseline, 28 days after vaccination given at different intervals	Day 28	Frequency and percentage of S protein-specific T cells response elicited by each of the regimens as measured by QuantiFERON at baseline and 28 days after vaccination
NT50 GMT against SARS-Cov-2 pseudovirus (pVNT) Omicrron strain at baseline 28 and 90 days after vaccination	Day 0, 28 and 90	NT50 GMT against SARS-Cov-2 pseudovirus (pVNT) Omicrron strain at baseline 28 and 90 days after vaccination
GMFR changed from baseline in NT50 against SARS-CoV-2 pseudovirus (pVNT), Omicron strain at 28 and 90 days after vaccination	Day 28, 90	GMFR changed from baseline in NT50 against SARS-CoV-2 pseudovirus (pVNT), Omicron strain at 28 and 90 days after vaccination

Countries

Thailand

Outcome results

None listed

Source: ClinicalTrials.gov · Data processed: Feb 4, 2026