An interesting study in The Lancet published 25th June 2021 by Liu and others confirmed that people who had been vaccinated with the Oxford AstraZeneca vaccine initially and then with the Pfizer based vaccine following had a nine times more antibody response than those who stuck to the same AstraZeneca vaccine.

830 participants were enrolled and randomised including 463 with a 28 day prime boost interval first.  

Participant mean age was:

  • 57.8 years old, 45.8% were female 
  • 25.3% from ethnic minorities.  

The study found that at 28 days post SARS-CoV-2 anti-spike IgG in the AstraZeneca Pfizer recipients, the response was non inferior to that of the AstraZeneca recipients with a ratio of 9.2.  

Interestingly enough, in participants primed with the Pfizer vaccine, the ratio was less with only a geometric mean ratio of 0.51 if followed by the second dose as an AstraZeneca vaccine.  

T-cell response at 28 days post boost in the AstraZeneca first dose, Pfizer second dose group was 185. This is in comparison to 50 in the AstraZeneca first and second doses, 80 in the Pfizer and Pfizer second doses and 99 in the first Pfizer and then AstraZeneca second dose.

There were, however, four serious adverse events across all the groups but none of these were considered related to immunisation.  

The authors concluded that this study proved that there should be flexibility in the use of first dose vaccines and second dose.

Dr Paul Ettlinger

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