BENGALURU: As per a study published in The Lancet journal on March 8 on the safety and immunogenicity of the Phase-2 trials of Covaxin (BBV152), the primary outcome was that neutralising antibody titers and seroconversion rates were four fold higher at four weeks after the second dose (day 56). Seroconversion is when antibodies become present in the blood.
“In the Phase-1 trial, BBV152 induced high neutralising antibody responses that remained elevated in all participants at three months after the second (dose). In Phase-2, (it)showed better reactogenicity and safety outcomes, and enhanced humoral and cell-mediated immune responses compared to Phase-1,” the study said.
Simply put, Dr Ravindra Mehta, senior consultant and HOD, Pulmonology and Interventional Pulmonology, Apollo Speciality Hospitals said, neutralising antibodies are the most important antibodies which neutralise the Covid attack. “In Phase-2, the study states that the vaccine activates all parts of the immune response, be it to curtail the infection at an early stage or even long term. If the body is re-challenged with the virus later, it will a have long-term memory of antibody response,” he said.
Due to the difference in dosing regimens between Phase-1 (two doses given two weeks apart) and Phase-2 (two doses given four weeks apart) trials, neutralisation responses were significantly higher in Phase-2. Additionally, the proportion of participants reporting adverse reactions in the Phase-2 trial were lower than in Phase-1.
However, it added that the results reported in this study do not permit efficacy assessments. Dr Mehta said immunogenicity referred to the ability to induce an immune response, while efficacy indicated to what percentage the vaccine can prevent the Covid infection.Commenting on the study, Dr Faheem Younus, Chief of Infectious Diseases at University of Maryland, tweeted: “380 volunteers studied, Double-blind, RCT trial 2 shots - 28 days apart, No serious (level 4/5) side effects. Can’t determine efficacy by phase 2 trials but it’s safe/ immunogenic (sic).”