* Officials mull second doses for children
* Mixed approach could give alternatives to second Pfizer
dose
* Pfizer shot's myocarditis risk prompts caution
* Full results of adult trial due shortly -investigator
By Alistair Smout
LONDON, Sept 17 (Reuters) - A British study will look into
the immune responses of children to mixed schedules of different
COVID-19 vaccines as officials try to determine the best
approach to second doses in adolescents given a small risk of
heart inflammation.
Children aged 12-15 in Britain will be vaccinated from next
week, while those aged 16-17 have been eligible for shots since
August.
However, while the children will be offered a first dose of
the Pfizer-BioNTech vaccine, officials have
said that advice about second doses will be given at a later
date, while more data is gathered.
Britain's Joint Committee on Vaccination and Immunisation
(JCVI) initially declined to recommend shots for all 12- to
15-year-olds, citing uncertainty over the long-term impact of
myocarditis, a rare side effect of mRNA-based vaccines such as
Pfizer's. The heart condition typically resolves itself with
mild short-term consequences, health experts have said.
Hong Kong has advised children only get one shot, owing to
similar concerns over heart inflammation.
The study, called Com-COV3, will test different vaccine
schedules in 12- to 16-year-olds, looking at the immune
responses and milder side-effects.
"The concern here is about the risks of myocarditis,
particularly with the second dose with Pfizer vaccine in young
men," the trial's lead researcher, Matthew Snape of the Oxford
Vaccine Group, told reporters.
"This will provide the JCVI with information crucial to
informing their advice about immunising teenagers in the UK," he
said.
The trial will give all participants a first dose of the
Pfizer-BioNTech vaccine. That will be followed eight weeks later
by either a second full dose or a half dose of the Pfizer shot,
a full dose of Novavax's vaccine or a half dose of
Moderna's shot.
The trial is recruiting 360 volunteers, not large enough to
directly assess the myocarditis risk of the different
combinations, which Snape said was 1 in 15,000 after two doses
of the Pfizer shot in young men.
But, he added, it "would be reassuring to see if there was a
lower inflammatory response after one of these changes compared
to Pfizer (followed by) Pfizer," and that it might be
"reasonable to infer that the risks of myocarditis might be
lower" in such an instance.
Snape is running another arm of the trial in adults, giving
mixed vaccine schedules both four and 12 weeks apart, and
comparing the responses. He said the results of that would be
coming "very shortly".
(Reporting by Alistair Smout
Editing by Bill Berkrot)