Heterologous boosting

Heterologous boosting

Subject: Science and Technology

Context: Mixing Covishield and Covaxin, the two main vaccines against Covid-19 in use in India, has found by a new ICMR study to be safe and also to provide better immunity.

Concept:

Heterologous boosting

• The idea of heterologous boosting initially emerged in Europe,.
• Vaccine platforms may vary in their ability to induce antibody and T-cell response
• If one platform induces a predominantly antibody response, experts say it can be followed by a platform that induces predominantly a T cell response (e.g. vector and DNA vaccines Such heterologous strategies are being studied in HIV, malaria, flavivirus (e.g. dengue), HPV, Ebola and influenza.

Mixing Covishield and Covaxin

• Covishield is an adenovirus vector platform-based vaccine, while Covaxin is an inactivated whole virus vaccine.
• This study demonstrates that immunisation with a heterologous combination of an adenovirus vector platform-based vaccine followed by an inactivated whole virus vaccine is safe and elicits better immunogenicity than two doses of homologous vaccination, using the same vaccines
• Covishield will trigger only an anti-spike protein response (and of course anti -adenovirus response). Covaxin used as a booster in principle should boost anti-spike response further and generate a primary response against all other SARS-CoV-2 proteins which are part of the Covaxin preparation
• The ICMR data in the preprint shows that heterologous vaccination can indeed trigger an anti-N-protein response due to a boost with Covaxin. However further data will be needed to state that heterologous vaccination strategy for Covishield and Covaxin combination is useful

Impact

• According to the World Health Organization, there is currently limited data on the immunogenicity or efficacy of a “mix and match” regimen.
• Experts caution that mixing should not be randomly done but should be based on understanding multiple issues.