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* Both mixed schedules produced more antibodies than two AZ
shots
* Results support move towards mix-and-match approach in
Europe
* Professor: don't abandon clinically approved schedules
(Adds official on implications for vaccine rollout)
By Alistair Smout
LONDON, June 28 (Reuters) - 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, an
Oxford study said on Monday.
The 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.
Matthew Snape, the Oxford professor behind the trial, said
that the findings could be used to give flexibility to vaccine
rollouts, but was not large enough to recommend a broader shift
away from clinically approved schedules on its own.
"It's certainly encouraging that these antibody and T-cell
responses look good with the mixed schedules," he told
reporters.
"But I think your default has to stay, unless there's a very
good reason otherwise, to what is proven to work," he added
referring to the same-shot vaccine schedules assessed in
clinical trials.
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 Britain, officials have suggested an 8-week gap between
vaccine doses for over-40s and a 12-week gap for other adults.
"Given the UK’s stable supply position there is no reason to
change vaccine schedules at this moment in time," England's
Deputy Chief Medical Officer Jonathan Van-Tam said, adding that
the data on a 12-week interval would influence future decisions
on the rollout programme.
Over 80% of adults in Britain have now received one dose of
COVID-19 vaccine and 60% have had two shots.
(Reporting by Alistair Smout; editing by Michael Holden, Guy
Faulconbridge and Gareth Jones)
