Mix-match method boosts immune response of AstraZeneca jab: Study

A mixed schedule of vaccines where a shot of Pfizer’s COVID-19 vaccine is given four weeks after an AstraZeneca shot will produce better immune responses than giving another dose of AstraZeneca, according to a new study.

The Oxford University study, called Com-COV, compared mixed two-dose schedules of Pfizer and AstraZeneca vaccines, and found that in any combination, they produced high concentrations of antibodies against the coronavirus spike protein.

The data provides support for the decision of some European countries that have started offering alternatives to AstraZeneca as a second shot after the vaccine was linked to rare blood clots.

Professor Matthew Snape, associate professor in paediatrics and vaccinology at the University of Oxford, and chief investigator on the trial, said: “The Com-COV study has evaluated ‘mix and match’ combinations of the Oxford and Pfizer vaccines to see to what extent these vaccines can be used interchangeably, potentially allowing
flexibility in the UK and global vaccine rollout.

“The results show that when given at a four-week interval both mixed schedules induce an immune response that is above the threshold set by the standard schedule of the Oxford/AstraZeneca vaccine.”

The highest antibody response was seen in people receiving two doses of Pfizer vaccine, with both mixed schedules producing better responses than two doses of AstraZeneca vaccine.

An AstraZeneca shot followed by Pfizer produced the best T-cell responses, and also a higher antibody response than Pfizer followed by AstraZeneca.

The results were for combinations of vaccines given at four week intervals to 830 participants.

Com-COV is also looking at mixed schedules over a 12-week interval, and Snape noted that AstraZeneca’s shot was known to produce a better immune response with a longer interval between doses.

In the UK, officials have suggested an 8-week gap between vaccine doses for over-40s and a 12-week gap for other adults.

‘Vital step forward’

England’s Deputy Chief Medical Officer Jonathan Van-Tam said the results of the Com-COV study were a “vital step forward”.

“They offer supportive evidence that the standard (non-mixed) JCVI (Joint Committee on Vaccination and Immunisation) recommendations for COVID-19 vaccination all produce highly satisfactory immune responses, for both main vaccines in use,” he said.

“Given the UK’s stable supply position there is no reason to change vaccine schedules at this moment in time.”

More than 80 percent of adults in the UK have now received one dose of COVID-19 vaccine and 60 percent have had two shots.