January 4, 2021

expert comment on combining different COVID-19 vaccine doses

Comments from scientists on combining different COVID-19 vaccines in a heterologous prime-boost regimen.

Prof Helen Fletcher, Professor of Immunology at the London School of Hygiene & Tropical Medicine, said:

“We are fortunate to have a first generation of COVID-19 vaccines that are highly effective. For many diseases, such as HIV, TB and malaria, the immune response to one vaccine is not sufficient to provide a high level of protection so the next logical step is to combine two different vaccines delivering the same antigen in a heterologous prime-boost regimen.

“In a heterologous prime-boost we would give the spike protein using one vaccine platform and then present the same spike protein using a different vaccine platform – this could give a much stronger immune response to the spike because the second vaccination isn’t limited by any anti-vector immune response.

“Heterologous prime-boost regimens would be an important strategy to explore in clinical trials if the first generation of COVID-19 vaccines had been weakly protective, as combining vaccines could boost the level and duration of efficacy. Where efficacy is already >90% there is little advantage to pursuing a heterologous prime-boost regimen, although if heterologous boosting extended the duration of efficacy it would be worthwhile. Based on previous studies which combine different vaccine types, a combination of the AZ and Pfizer vaccines is likely to be safe but it’s important that this is tested in the context of a clinical vaccine trial.”

All our previous output on this subject can be seen at this weblink:

www.sciencemediacentre.org/tag/covid-19

Declared interests

Prof Helen Fletcher: “I am a trustee of the Jenner Vaccine Foundation and Director of International development, UKRI.”