Sanofi’s SARS-CoV-2 adjuvanted recombinant protein-based vaccine (COVID-19 candidate vaccine), developed in collaboration with GSK, has been administered to 440 adults in a first trial-a phase 1/2 trial (VAT00001).The first trial assessed the safety of the candidate vaccine and its capability to induce an immune response to help identify an optimal vaccine dose. Interim results from this trial showed a lower than expected antibody response to the vaccine, especially in individuals aged 60 years and older, in combination with a higher than expected reactogenicity.

Based on these observations, it is necessary to assess optimized antigen formulations to select a formulation that will progress to the next clinical steps. This is the objective of a phase 2 trial (VAT00002).2

Our phase 2 trial

Study status: ongoing, recruitment process: complete

This trial will assess the reactogenicity and safety of three different antigen concentrations combined with a set dose of AS03 adjuvant, as well as their capacities to induce immune responses. 

The trial will be conducted in the US and Honduras and will include a total of 720 participants-one half will be 18-59 years of age and the other half 60 years of age or older.

All participants in this study are monitored for one year.

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

To participate in this new phase 2 trial, volunteers must be 18 years old or older, willing, and able to attend all trial visits and perform medical procedures. Participants with high-risk medical conditions or those with a previous history of COVID-19 will be eligible to participate in the trial. Participants’ eligibility will be tested at the start of the trial.

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

Eligible volunteers will be assigned randomly to receive one out the three vaccine formulations. There is no placebo in this trial.

How does the Trial Work?

  • Participants will receive two injections of the same vaccine formulation three weeks apart. Neither participants nor study clinicians will know which formulation is given to participants. At the end of the trial, if a safe and efficient vaccine formulation is approved for use by the local regulatory authorities, participants who received a formulation considered less effective than that approved will be offered the approved vaccine. 
  • Blood samples will be collected at different timepoints during the trial to assess the strength of the immune response after vaccination. 
  • After the first vaccine injection, all participants will be monitored through medical check-ins by trial staff on a regular basis (or more frequently if a SARS-CoV-2 infection is confirmed or suspected) during the entire trial.
  • Participants will be followed for a duration of approximately 365 days after the second injection.

Benefits and risks

The full benefit and risks of these candidate vaccine formulations are currently not completely understood. This trial is fundamental to determine the impact of a vaccine candidate that has the potential to help control the pandemic and reduce both the individual and public health burdens of COVID-19 illness and SARS-CoV-2 infections.


1 VAT00001 Study (more details available at
2 VAT00002 Study (more details available at

MAT-GLB-2100643 v1.0 FEB 2021