Immunogenicity of Heterologous Versus Homologous Prime Boost Schedule With mRNA and Inactivated COVID-19 Vaccines

Immunogenicity of Heterologous Versus Homologous Prime Boost Schedule With mRNA and Inactivated COVID-19 Vaccines: a Single-blinded, Randomized, Parallel Group Superiority Trial

This study is a randomized, simple-blinded comparative phase III clinical trial comparing the immunogenicity of two doses Coronovac to that of a first dose of Coronovac (Sinovac, Beijing, China) followed by a booster shot with the mRNA-based BNT162b2 SARS-CoV-2 vaccine (Comirnaty, Pfizer-BioNTech).

The purpose of this study is to evaluate the superiority, safety and immunogenicity of the heterologous prime-boost CoronaVac/BNT162b2 vaccination to the homologous CoronaVac/CoronaVac regimen.

This study is a randomized simple-blinded comparative phase III clinical trial in COVID-19 vaccine naïve volunteers adults aged between 18 and 60 years. The purpose of this study is to evaluate the superiority, safety and immunogenicity of the heterologous prime-boost CoronaVac/BNT162b2 vaccination to the homologous CoronaVac/CoronaVac regimen. The study is conducted in four different sites located in the North of Tunisia.

A total of 240 eligible participants were included. Among them, the primary end point data were available for 100 participants randomly allocated to heterologous boost group versus 99 participants randomly allocated to homologous boost dose group.

Participants are assigned to receive either two injections of the CoronaVac vaccine (1st and 2nd vaccine), or CoronaVac as 1st dose and Pfizer as 2nd dose in 3 to 4 weeks interval.

A blood sample (5ml of the whole blood) is collected for each participant at the vaccination center before the first dose injection. After verifying the absence of a SARS-CoV-2 infection during the interrogation (a follow-up survey), a 2nd blood sample (5ml of whole blood) is taken for each participant at the vaccination center before the second dose injection. After the two injections, a 3rd blood sample (5ml of whole blood) will be taken for each participant between day 21 and day 35 after the second dose. Data collection and all samples are treated at Institute Pasteur of Tunis.

Inclusion Criteria:

• Acceptance to participate in the study.
• Age: 18-60 years old.

Non-inclusion criteria:

• Presence of disability (mainly mental disability).
• Pregnancy.
• Patients under immunosuppressive treatment or immunocompromised individuals.
• Prior Covid-19 infection.

Exclusion Criteria:

• Occurrence of a serious adverse event (death, anaphylactic shock, ...).
• Subjects wishing to withdraw from the study.
• Occurrence of a SARS-CoV-2 symptomatic infection during the follow-up period.