The phase 3 trial follows positive initial results from a phase 2 clinical trial (VAT00002)1. In that trial, the COVID-19 vaccine candidate was administered to 722 adults to assess the safety, reactogenicity and immunogenicity of 3 doses and to identify an optimal vaccine dose. Results showed strong rates of neutralizing antibody response with 95% to 100% seroconversion following a second injection in all age groups (18 to 95 years old), across all doses2.

A 10µg antigen formulation of the SARS-CoV-2 adjuvanted recombinant protein-based vaccine developed by Sanofi in combination with GSK’s AS03 adjuvant is under evaluation in a phase 3 trial (VAT00008)3 regarding efficacy, immunogenicity and safety of the vaccine candidate compared to a placebo. 

For more information on the phase 3 clinical trial per country, please refer to the following contact list:

Call center number: +57 01800091133

India and Nepal
Call center number: 1800 22 2295 (toll-free)


Call center number: 1-800-633-1610
Sanofi Trial Transparency mailbox:

Ghana and Kenya
Vaccines Medical Information contacts:
+254 20 5139600 / +254 733 825000/
+254 725 801128

Call center: +5073041800 / +5073829500


Our phase 3 trial

Study status: ongoing, recruitment process: ongoing

The trial is conducted in 2 stages, the first with a monovalent (single antigen) vaccine comprising the spike protein of the original SARS-CoV-2 virus (D614) and the second stage with bivalent (2-antigen) vaccine comprising the original spike protein and the beta variant (B.1.351). 

Participants are categorized as naïve (not previously infected) and non-naïve (evidence of previous infection) based on serological and virological ascertainment of prior SARS-CoV-2 infection at the time of vaccination. 

The primary objective is the prevention of symptomatic COVID-19 with onset at least 14 days after the second injection of the vaccine in SARS-CoV-2 naïve individuals. Safety of the vaccines will be evaluated throughout the study compared to placebo. Secondary endpoints include severe COVID-19 disease and asymptomatic infection.

The entire study plans to enroll approximately 21000 participants.

Participants are randomized equally to either the investigational study vaccine (monovalent or bivalent vaccines) or placebo.  

The study targets recruitment of racial and ethnic diversity that will be representative of the countries in which the study will be conducted. The study has a follow-up of 13 months.  

Data on VAT08 efficacy with the monovalent formulation containing the original strain are showing an efficacy of 57.9% (95% confidence interval [CI, 26.5, 76.7]) against any symptomatic COVID-19 disease in the seronegative population. The candidate vaccine provided 100% protection against severe disease and hospitalizations and 75% efficacy against moderate-to-severe disease4

Sequencing is in progress, but early data indicate 77% efficacy against any delta variant-associated symptomatic COVID-19 disease4.

The vaccine candidate was well-tolerated in younger and older adults with no safety concerns4

The phase 3 study is still ongoing for evaluating the efficacy of its bivalent formulation as primo-vaccination. 

Eligibility criteria

Aged 18 years old or older

Able to attend all the trial visits and perform medical procedures

Participants with high-risk medical conditions or those with a previous history of COVID-19 will be eligible

Participants’ eligibility is assessed at inclusion. To participate in this new Phase 3 trial, volunteers must be 18 years old or older, willing, and able to attend all trial visits and perform medical activities. Individuals with high-risk medical conditions (e.g. diabetes, hypertension, cancer…) are eligible for participation. 

Individuals currently participating in another trial, or who have previously received a vaccine against COVID-19 are not eligible for this trial. At this stage of the vaccine development, women who are pregnant or breastfeeding are not yet eligible. 

How does the Trial Work?

  • At the time of enrollment, blood and nasopharyngeal samples are obtained to determine whether the participant is SARS-CoV-2 naïve or not.
  • Participants are randomized to receive two injections of the candidate-vaccines or placebo, 3 weeks apart. Neither participants nor study clinicians will know which formulation is given to participants. 
  • Blood samples will be collected at different timepoints during the trial to be able to assess the strength of the immune response after vaccination and the efficacy of the vaccine preventing SARS-CoV-2 infection compared to placebo. 
  • After the first vaccine injection, all participants will be monitored by trial staff on a regular basis (or more frequently in a SARS-CoV-2 infection or suspected COVID-19) during the entire trial. 
  • Participants will be followed for a duration of approximately 365 days after the second injection

Access to authorized/approved COVID-19 vaccine

  • Before enrolling in this study, if an authorized/approved COVID-19 vaccine is available and the participant is eligible to receive it, the study team will encourage the participant to take it. Volunteers can join the study if they have no intention of getting the authorized/approved COVID-19 vaccine at the time.
  • At any time during the study, participants are encouraged to take an authorized/approved vaccine when a vaccine becomes available to them and are encouraged to speak to the study team about their decision.
  • If one of the study vaccines is determined to be safe and effective, the protocol will be amended in consultation with National Health Authorities to a blinded cross-over study design to ensure that all participants are offered a study vaccine. 

This trial is fundamental to determine the full benefit and risks of these candidate vaccine formulations and the impact it may have to help manage and control the pandemic, reducing both the individual and public health burden of COVID-19.

The goal of this study is to generate data required for approval of each of the vaccines for use in prevention against SARS-CoV-2 infection and disease in adults. The data collected during this study will also support future development in other populations (eg, pediatrics, pregnant women).


  1. VAT00002 Study available at
  2. Sridhar S, et al. Lancet Infect Dis 2022;S1473-3099(21)00764-7.
  3. VAT00008 Study available at 
  4. Sanofi and GSK to seek regulatory authorization for COVID-19 vaccine. Available at:

MAT-GLB-2102357 V2.0 – March 2022