India has announced the distribution of “precautionary doses” against Covid for healthcare and frontline workers, as well as individuals over 60 years of age with comorbidities. Although India has not approved a heterologous or mix-and-match use of vaccines, several experts claim that heterologous vaccines would work better against Covid.
Dr Samiran Panda, the Head of the Epidemiology and Infectious diseases division at the Indian Council of Medical Research (ICMR) told The Sunday Guardian, “The scientific evidence from different countries and studies is underlining the advantages of the heterologous approach of vaccination. However, we need to look at which vaccines are to be mixed and matched and also, the approach depends on vaccine availability.”
Similarly, immunologists think that heterologous doses will help fight the virus. “There is no question that the third dose, also known as the precautionary dose, will boost Covid immunity and should be recommended. The question is when the dose should be administered and what type of vaccine should be used—homologous or heterologous, depending on the vaccine’s availability. When selecting a vaccine, two factors must be considered: testing its safety and efficacy. Safety should not be compromised in the third dose,” Dr Santasabuj Das, who works in the field of immunology and is currently Director-in-charge of the ICMR-National Institute of Occupational Health, Ahmedabad, Gujarat, told this correspondent.
“In a small group of the population, a heterologous dose was administered and it was more effective against Covid,” Dr Das stated, referring to several research and trials that demonstrated that heterologous vaccines enhanced antibody response. As a result, the studies show that the heterologous dose is just as effective as, if not more, the homologous dose. “So, based on the findings, heterologous boosting is effective, although the experiment may not have covered a broad horizon because it was conducted on a limited population,” he added. In addition, genetic history and microbiome have an impact on vaccine efficiency. Furthermore, the virus is more lethal in cold conditions, compromising the immunity of the body.
Professor of Microbiology at Jagannath Gupta Institute of Medical Sciences & Hospital, Kolkata, Dr Nishith Kumar Pal told this newspaper, “The heterologous dose will expand the number of antigens used in the vaccine. The vaccines are always maintained in the cold chain and a long exposure of the vaccine to the adverse temperature might affect the efficacy of the vaccine.”