This article will briefly discuss the safety and immunogenicity of Covaxin as published in The Lancet on 21.01.2021.

Background information:

Usually, whole-virion inactivated vaccines are formulated with Alum, which does not have the ability to induce cell-mediated responses. To stimulate cell-mediated responses, an imidazoquinoline molecule which is a toll-like receptor (TLR) 7/8 agonist, has been used in this vaccine.

Algel-IMDG (an imidazoquinoline molecure chemisorbed on alum (Algel)) has been designed to traffic vaccine antigen directly to draining lymph nodes without diffusing into the systemic circulation.

One of the desirable features for COVID-19 vaccines is the ability to induce T-helper-1 cell (Th1) responses.

Key Messages:

The technical name for the Bharat Biotech vaccine against SARS-CoV-2 is BBV152. It is a whole-virion beta-propiolactone-inactivated SARS-CoV-2 vaccine adjuvanted with Algel-IMDG. The virus strain (NIV-2020-770) used in the vaccine contains the Asp614Gly mutation and was provided to Bharat Biotech by the ICMR NIV. The candidate vaccines were formulated with two adjuvants: Algel (alum) and Algel-IMDG, an imidazoquinoline class molecule (TLR7 and TLR8 agonist) adsorbed onto Algel. The control group contained only a sterile phosphate-buffered solution and Algel.

Prior to research on humans, studies were done in mice, rats, and rabbits to assess vaccine safety profile, and humoral and cell-mediated responses. Thereafter, two live viral challenge protective efficacy studies were done in hamsters and non-human primates wherein virus was rapidly cleared from upper and lower respiratory tract. There was no lung pathology after viral challenge.

The phase 1 trial described in the Lancet article was intended to determine which two formulations (of three tested in the trial) would progress to the phase 2 trial.