Prime-boosting is the concept of using different vaccines sequentially to deliver the same antigen to elicit a maximum T-cell memory (cellular immune) response.
An article in “Trends in Immunology” reviews the topic. It notes that while there have been many vaccine successes, there are other diseases such as HIV, TB and malaria which “resist the humoral (antibody-based) immunity that is characteristically generated by traditional vaccines.”
“Over the past few years, significant effort has been directed to promote potent cellular immunity to these pathogens. One effective technique is the ‘prime-boost’ strategy which involves priming the immune system to a target antigen delivered by one vector and then re-administering the antigen using a different vector.”
The logic behind prime-boosting is that the subject develops some immunity to the first vector and this inhibits “robust antigen presentation” when the same vaccine is used to boost.
An example in the context of COVID vaccination may be giving the Oxford vaccine, which uses an adenovirus to deliver the spike antigen, and then boost possibly with a molecular clamp vaccine, such as the one being developed by the University of Queensland.