A triple-blinded randomized control trial to evaluate the safety and immunogenicity of fractional doses of COVID-19 vaccines (ChAd0x1, AD26.COV2. S, and BNT162B2) among Nigeria adults: the SIFCoVAN trial.

BACKGROUND

The COVID-19 pandemic posed a major public health challenge with varying devastating effects on the global community. Vaccination is the most effective measure in combating this pandemic. A major challenge, especially in resource-limited settings, was the shortage of the vaccines. However, evidence by WHO in the use of fractionated doses in combating yellow fever prompted the evaluation of the safety and immunogenicity of fractionated doses of COVID-19 vaccines (ChAd0x1, AD26.COV2.S, and BNT162B2) among Nigerian adults (18-65 years).

METHODS

This is a multi-center, non-inferiority randomized, triple-blind trial involving 1812 COVID-19 vaccine naïve participants. Six hundred four eligible participants will be randomized into each of the three vaccine arms of ChAd0x1, AD26.COV2.S, and BNT162B2 COVID-19 vaccine. 151 participants will be randomized each into the 25% and 50% fractionated dose and 300 in the standard full dose arm for the ChAd0x1 and AD26.COV2.S group. In the BNT162B2 group, 201 participants will be randomized into the 50% fractionated dose and 403 into the standard dose arms. The efficacy (immunogenicity) will be evaluated by collecting blood samples at baseline (day 0) and day 28 after immunization to determine the geometric mean fold rise (GMFR) of ≥ 2.5 within the range of 20% non-inferiority to the standard dose of anti-SARS-CoV-2 S antibody response detected by ELISA termed as seroconversion. Safety and adverse events will be evaluated through active evaluation during the first 72 h of vaccine administration and on days 14 and 28 of clinic visits. The trial will also assess secondary immunogenicity variables of 50% plaque plaalite reduction neutralization by antibodies against SARS-CoV-2 variants (α, δ, and κ) and cytokines production (IFNα, γ, and IL-2 producing CD4 and CD8 T lymphocytes).

DISCUSSION: The proposed trial will allow for a comprehensive understanding of the immunologic responses and safety profile of fractional doses compared to full doses of COVID-19 vaccines among Nigerian adults. In addition, this will guide policy implementation for prompt vaccination of the population to maximize access to the limited vaccines available during the COVID-19 pandemic or future epidemics/pandemics.

TRIAL REGISTRATION: The study is registered at the Pan African Clinical Trials Registry (PACTR), a primary registry in the WHO International Clinical Trial Platforms. PACTR202206754734018. Registered on June 1, 2022, Accessible at: https://pactr.samrc.ac.za/ Trial Sponsor: Open Philanthropy.