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* Britain asks regulator to assess shot for rollout
* Philippines says it will secure millions of doses
* Experts raise doubts over robustness of trial results
* AstraZeneca CEO says likely to run an extra global trial
* EXPLAINER-Vaccine trial efficacy numbers:
By Alistair Smout and Karen Lema
LONDON/MANILA, Nov 27 (Reuters) - Britain gave AstraZeneca's
COVID-19 vaccine a vote of confidence on Friday when it asked
its regulator to assess the shot for a rollout after experts
raised questions about trial data and the company said it may
run another study to gauge efficacy.
The UK government has secured 100 million doses of the
vaccine, developed by AstraZeneca and Oxford University,
the most it has ordered of any shot to fight a pandemic that has
killed more than 1.4 milion people globally.
The British drugmaker expects 4 million doses to be
available in the country by the end of next month, and Health
Secretary Matt Hancock aims for a rollout to begin before
Christmas.
"We have formally asked the regulator to assess the
Oxford/AstraZeneca vaccine, to understand the data and determine
whether it meets rigorous safety standards," Hancock said.
"This letter is an important step towards deploying a
vaccine as quickly as safely possible."
Britain's Medicines and Healthcare products Regulatory
Agency (MHRA) started an accelerated "rolling review" of the
vaccine at the start of this month as data comes in on safety
and efficacy.
In the global race to develop vaccines against COVID-19,
AstraZeneca's candidate is viewed as offering one of the best
hopes for many developing countries because of its cheaper price
and ability to be transported at normal fridge temperatures.
Officials in the Philippines said on Friday they would
secure 2.6 million AstraZeneca shots - the country's first
supply deal for a COVID-19 vaccine - and were negotiating a
possible purchase of a further 1 million doses.
The announcements came after some scientists raised doubts
about the robustness of results showing the shot was 90%
effective in a sub-group of trial participants who, by error
initially, received a half dose followed by a full dose.
AstraZeneca had released trial data on Monday that showed
its experimental vaccine prevented on average 70% of COVID-19
cases in late-stage trials in Britain and Brazil.
While the success rate was 90% in the sub-group, some
experts said the relatively small number of participants made it
harder to be confident in the findings.
AstraZeneca said the administering of the half dose had been
reviewed and approved by independent data safety monitors and
the UK regulator, adding that the regulator publicly confirmed
there was "no concern".
The success rate of 62% when the full dose was given twice,
as it was for most participants, is still above the 50% required
by U.S. regulators. Europe's drug regulator has said it will not
set a minimum level of efficacy.
If a vaccine has an efficacy of 50%, it means that if 100
people who haven't been exposed to the virus are immunised with
it, on average, 50 of them would not get infected.
CEO Pascal Soriot said on Thursday, though, that the
drugmaker was likely to run an additional global trial to assess
the efficacy of its vaccine using the lower dosage.
A spokesperson for Oxford University said additional data
from international trials would help researchers assess the
vaccine's efficacy among a more diverse population.
EXPLAINER-Trial efficacy numbers:
CONFUSION 'PROBLEMATIC'
Pauline Londeix, co-founder of French drug transparency
group OT-Med, said apparent confusion over the trial results was
"very problematic for public confidence in vaccines".
"It has largely to do with the race drugmakers are engaged
in currently, which leads them to present vaccine candidates in
the best possible way and not release full protocols and
results. It is the opposite of what is needed in our view."
Nonetheless, Britain's top science adviser said the interim
results showed the AstraZeneca vaccine was successful.
"The headline result is the vaccine works and that's very
exciting," Patrick Vallance said on Thursday during a news
conference with Prime Minister Boris Johnson.
Only 2,741 volunteers were in the sub-group of the
AstraZeneca-Oxford trial that gave the 90% efficacy read-out, a
fraction of the tens of thousands in trials that resulted in the
above-90% efficacy data released earlier this month for
Pfizer-BioNTech's and Moderna's vaccines.
"Sub-group analyses in randomised controlled trials are
always fraught with difficulties," said Paul Hunter, a professor
of medicine at Britain's University of East Anglia.
"In order to have faith in the results," Hunter added, any
sub-group analysis "should be sufficiently powered" with large
numbers of volunteers.
'NUMBER OF VARIABLES'
Shares in AstraZeneca were down 0.7% at around 1055 GMT.
They have fallen about 7% since it reported the vaccine data on
Monday.
Vaccine optimism helped buoy the stock to record peaks this
year, making the drugmaker the most valuable listed British
company, but its shares have lost over 17% since late July and
it has fallen behind Unilever and Shell.
In contrast to AstraZeneca's drop this week, Moderna
shares have rallied 22% since it released its vaccine
trial data on Nov. 16 and Pfizer and BioNTech
are up 6% and 14% respectively since announcing data on Nov. 9.
A peer-reviewed analysis of data from the AstraZeneca-Oxford
trial will be published in The Lancet in coming weeks.
The U.S. Food and Drug Administration (FDA), has not
commented on AstraZeneca's vaccine trial results. The European
Medicines Agency said on Thursday it would "assess data on the
efficacy and safety of the vaccine in the coming weeks once they
have been received from the company".
Moncef Slaoui, chief scientific adviser for the U.S.
government's vaccine programme Operation Warp Speed, has also
highlighted gaps in the interim trial data.
He said no-one in the sub-group that got the initial half
dose was older than 55 - suggesting that regimen's efficacy in
older age groups was unproven.
"There are a number of variables that we need to understand,
and what has been the role of each one of them in achieving the
difference in efficacy," Slaoui told a briefing on Tuesday.
(Reporting by Alistair Smout in London and Karen Lema in
Manila; Additional reporting by Kate Kelland in London and
Matthias Blamont in Paris; Writing by Pravin Char; Editing by
Carmel Crimmins)
