* Britain has extended gap to second dose to 12 weeks
* AstraZeneca has hailed this as 'sweet spot' for efficacy
* Data on efficacy in older people still lacking
(Adds detail, quote)
By Alistair Smout
LONDON, Feb 2 (Reuters) - Oxford University and
AstraZeneca's COVID-19 vaccine showed in a study it had 76%
efficacy against symptomatic infection for three months after a
single dose, which increased if the second shot is delayed,
backing Britain's vaccine rollout policy.
The findings of the pre-print paper, which had not been
peer-reviewed, supported Britain's decision to extend the
interval between initial and booster doses of the shot to 12
weeks, Oxford said on Tuesday.
However, the new study did not address concerns about a lack
of data on efficacy among the oldest, who the British government
have given highest priority in its vaccine rollout.
Andrew Pollard, Chief Investigator of the Oxford Vaccine
Trial, said the data showed the 12-week interval between doses
was "the optimal approach to roll out, and reassures us that
people are protected from 22 days after a single dose".
Britain has decided to vaccinate as many people as possible
as quickly as possible by lengthening the amount of time between
initial shots and booster shots to tackle the COVID-19 pandemic.
AstraZeneca's research chief has said 8-12 weeks between
doses seems to be the "sweet spot" for efficacy, contrasting
with U.S. drugmaker Pfizer, which has warned that the
vaccine it has developed with Germany's BionTech was
not trialled with such an interval.
The results for the AstraZeneca/Oxford vaccine, gathered
from trials in Britain, Brazil and South Africa, showed that
immune responses were boosted with a longer interval to the
second dose among participants aged 18 to 55 years.
"Vaccine efficacy after a single standard dose of vaccine
from day 22 to day 90 post vaccination was 76%, and modelled
analysis indicated that protection did not wane during this
initial 3 month period," Oxford academics said in the preprint.
The paper said that vaccine efficacy was 82.4% with 12 or
more weeks to the second dose, compared to 54.9% for those where
the booster was given under 6 weeks after the first dose.
The longest interval between doses for those aged 56 and
over was between 6-8 weeks, so there was no data for the
efficacy of a 12 week dosing gap in that cohort.
Europe's medicine regulator has flagged that there is not
enough data to determine how well the vaccine will work in
people aged over 55, but Britain has expressed confidence the
vaccine works in all age groups.
The study said that no-one out of the 12,408 people
vaccinated with a single dose of the vaccine was hospitalised
with COVID-19 from 22 days after immunisation.
Oxford also said data seemed to suggest the vaccine reduced
transmission of infections, with a 67% reduction in positive
swabs among those vaccinated in the British arm of the trial.
(Reporting by Alistair Smout
Editing by Gareth Jones and Alexander Smith)
Astrazeneca (AZN)