EXPLAINER-Where are we in the COVID-19 vaccine race?

Dec 11 (Reuters) - Pfizer Inc and BioNTech SE
received U.S. regulatory authorization for their
COVID-19 vaccine on Friday, making it the first inoculation
against the new coronavirus to get a regulatory green light in
the United States.

The following is what we know about the race to deliver
vaccines to help end the coronavirus pandemic that has killed
1.59 million people worldwide:

WHO IS FURTHEST ALONG?

U.S. drugmaker Pfizer and German partner BioNTech
are the coronavirus vaccine trailblazers.

On Nov. 18, they became the first in the world to release
full late-stage trial data. Britain was the first to approve the
shot for emergency use on Dec. 3, followed by Canada on Dec. 9
and the U.S. Food and Drug Administration (FDA) on Dec. 11.

The European Medicines Agency (EMA) is due to complete its
review of the shot by Dec. 29 and India is accelerating its
review.

WHO WILL BE NEXT?

U.S. pharmaceutical company Moderna is ahead of the
pack at this point. It was next to release full data analysis
for a late-stage trial on Nov. 30, with its vaccine showing a
94.1% efficacy rate. FDA advisers are due to review it on Dec.
17 and the EMA will do so by Jan. 12.

WHO ELSE IS IN THE RUNNING?

Britain's AstraZeneca is seeking approval for its
vaccine in Britain after announcing interim late-stage trial
data on Nov. 23. It had an average efficacy rate of 70% and as
much as 90% for a subgroup of trial participants who got a half
dose first, followed by a full dose.

However, it is not clear how the regulator will deal with
the different dosages in the efficacy data in its assessment.
While India is conducting an accelerated review, it has asked
for more data. AstraZeneca is also in discussions with the EMA,
which is conducting a rolling review of the vaccine.

U.S. drugmaker Johnson & Johnson plans to deliver
trial data this year, or early in 2021, teeing it up for U.S.
authorization in February if its shot is effective. It reduced
the enrollment target for its clinical trial to 40,000
volunteers from 60,000 on Dec. 9, potentially speeding results
which are tied to how quickly participants become infected.

U.S. firm Novavax is running a late-stage trial in
Britain with data due in the first quarter of 2021. It expects
to start a large-scale trial in the United States this month.

France's Sanofi and Britain's GlaxoSmithKline
, however, announced a setback on Dec. 11 in their
attempts to develop a vaccine. The drugmakers said it showed an
insufficient immune response in older people in mid-stage trials
and that they would start a new study in February.

WHAT HAPPENS IN THE TRIALS?

The companies typically test their vaccines against a
placebo - typically saline solution - in healthy volunteers to
see if the rate of COVID-19 infection among those who got the
vaccine is significantly lower than in those who received the
dummy shot.

HOW ARE VOLUNTEERS INFECTED?

The trials rely on subjects becoming naturally infected with
COVID-19, so how long it takes to generate results largely
depends on how pervasive the virus is where trials are being
conducted. Each drugmaker has targeted a specific number of
infections to trigger a first analysis of their data.

HOW WELL ARE THE VACCINES SUPPOSED TO WORK?

The World Health Organization ideally wants to see at least
70% efficacy. The FDA wants at least 50% - which means there
must be at least twice as many infections among volunteers who
received a placebo as among those in the vaccine group. The EMA
has said it may accept a lower efficacy level.

WHAT ABOUT RUSSIA AND CHINA?

While Pfizer's shot was the first to be rolled out following
the publication of full Phase III trial data, Russia and China
have been inoculating their citizens for months with several
different vaccines still undergoing late-stage trials.

Russia said on Nov. 24 that its Sputnik V vaccine, developed
by the Gamaleya Institute, was 91.4% effective based on interim
late-stage trial results. It started vaccinations in August and
has inoculated more than 100,000 people so far.

AstraZeneca said on Dec. 11 that it would test a combination
of its vaccine with one of Sputnik V's two components to try to
boost the efficacy of the shot it is developing with Oxford
University.

China launched an emergency use programme in July aimed at
essential workers and others at high risk of infection. It has
vaccinated about one million people as of mid-November using at
least three shots - two developed by the state-backed China
National Biotec Group (CNBG) and one by Sinovac Biotech.

Sinovac said on Nov. 18 that mid-stage trial results showed
its CoronaVac shot triggered a quick immune response and interim
data from its late stage trial could come this year.

The Butantan Institute, a Brazilian biomedical centre, is
producing CoronaVac and aims to make 1 million doses a day ahead
of a vaccine campaign to be launched late January.

The United Arab Emirates, meanwhile, said on Dec. 9 that one
of the CNBG vaccines was 86% effective based on interim results
from a late-stage trial in the Gulf Arab state.
(Editing by Caroline Humer and David Clarke)