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* Real world study finds vaccine evasion of Omicron
* But impact is partially restored by booster with Pfizer
* Omicron reduces vaccine effectiveness by more than Delta
(Adds further detail, reaction)
By Alistair Smout
LONDON, Dec 10 (Reuters) - Booster COVID-19 shots
significantly restore protection against mild disease caused by
the Omicron variant, in part reversing an otherwise steep drop
in vaccine effectiveness, the UK Health Security Agency said on
Friday.
The early findings from a real-world analysis are some of
the earliest data on the protection against Omicron outside of
lab studies, which have shown reduced neutralising activity
against Omicron.
"These early estimates should be treated with caution but
they indicate that a few months after the second jab, there is a
greater risk of catching the Omicron variant compared to Delta
strain," said Dr Mary Ramsay, Head of Immunisation at the UKHSA,
adding that protection against severe disease was expected to
remain higher.
"The data suggest this risk is significantly reduced
following a booster vaccine, so I urge everyone to take up their
booster when eligible."
In an analysis of 581 people with confirmed Omicron, two
doses of AstraZeneca or Pfizer-BioNTech
vaccines provided much lower levels of protection against
symptomatic infection compared with what they provide against
Delta.
However, when boosted with a dose of Pfizer vaccine, there
was around 70% protection against symptomatic infection for
people who initially received AstraZeneca, and around 75%
protection for those who received Pfizer.
That compares with estimated protection against infection
from Delta following a booster of around 90%.
UKHSA reiterated it found that Omicron had a growth
advantage over Delta, and a 3-to-8 fold increased risk of
reinfection.
It said two UK studies which have yet to be presented
publicly and three international studies suggested Omicron gave
a 20 to 40-fold reduction in neutralising antibodies compared
with the viruses used to develop vaccines.
UKHSA said that while no cases of Omicron had yet resulted
in hospitalisation or death, the was insufficient data to assess
the severity of Omicron.
At current growth rates, Omicron would account for more that
50% of all COVID-19 infections by mid-December, UKHSA said, with
Britain exceeding one million infections by the end of the
month, as new measures come into force in England to slow the
spread of Omicron.
"Rising cases of the Omicron variant coupled with the new
data today should be a wake-up call for those who haven’t yet
had their booster or, indeed, any vaccine," National Health
Service medical director Stephen Powis said.
(Reporting by Alistair Smout; editing by James Davey and Andrew
Heavens)
