SCIENCE science.org 24 DECEMBER 2021 • VOL 374 ISSUE 6575 1543IN DEPTH
T
he new SARS-CoV-2 variant exploding
around the planet is forcing humanity
to adapt at a breakneck speed. Late
last week, countries across Northern
Europe imposed stringent new mea-
sures to try to bring down soaring
case numbers. The Netherlands issued a
near-complete lockdown of public life and
allowed residents to receive no more than
two guests per day—with an exception for
Christmas and New Year’s Eve, when four
visitors are allowed. Denmark, which lifted
all pandemic restrictions in September,
closed theaters, concert halls, museums,
and other public spaces and banned alcohol
sales after 10 p.m.
Driving those decisions is alarm at Omi-
cron’s wildfirelike spread—and caution in
the face of major uncertainty. If Omicron
makes people just as sick as the Delta vari-
ant, models predict a staggering rise of
hospitalizations—many times what most
health systems can handle. If Omicron
causes milder disease than Delta, things
would be less catastrophic—but even then,
“a considerable overload of the hospitals is
to be expected,” a group of experts warnedin a 19 December report to the German gov-
ernment. A massive Omicron wave might
also lead to many more cases of Long Covid.
It will take weeks before epidemiological
data deliver a clear verdict about disease se-
verity. But preliminary lab data, and a few
real-world clues, are raising hope among op-
timists, while others reserve judgment. “If
it turns out there is reduced severity from
Omicron, there are now potentially some
mechanisms that might help explain this,”
says Tom Peacock, a virologist at Imperial
College London (ICL). “On the other hand,
there may be some mechanisms that could
explain the opposite. So it’s still a bit of a
mess until the real-world data crystallizes.”
South Africa has seen only a modest
increase in hospitalizations for severe
COVID-19, even 1 month after cases started
to explode there. “We’re all still really cau-
tious about that data, but it seems to be
holding out,” says virologist Wendy Burgers
of the University of Cape Town. Moreover,
early signs suggest South Africa’s Omicron
wave may not last long. Cases are already
decreasing in Gauteng province, the out-
break’s epicenter, which is a bit of a mystery
given how transmissible Omicron seems to
be, says Trevor Bedford, a bioinformaticsspecialist at the University of Washington,
Seattle, and the Fred Hutchinson Cancer
Research Center. He suspects part of the ex-
planation is that more infections than usual
went unnoticed because they were mild or
asymptomatic, so the real peak was even
larger than official statistics showed.
But early data from Europe, which has
an older population than South Africa, are
less hopeful. Based on early hospitalization
data, for example, a report by modelers at
ICL concluded there are “at most limited
changes in severity compared with Delta.” “I
don’t know how to square these two things,
and that is probably giving me the most
pause at the moment,” Bedford says.
Lab data offer a little more hope. Anti-
bodies resulting from vaccination or infec-
tion have been shown to lose most of their
power against Omicron, but another immune
system defense—T cells, which recognize and
kill infected cells in the body—appears to do
better. Burgers and her colleague Catherine
Riou tested the response of T cells from peo-
ple who had received one or two doses of
the Johnson & Johnson COVID-19 vaccine
or two doses of Pfizer. In all three groups,
the T cell response to Omicron dropped by a
modest amount compared with the originalEarly lab studies shed light on Omicron’s behavior
Some data hint the new variant may be milder—but most scientists reserve judgment
COVID-By Gretchen Vogel and Kai KupferschmidtIMAGE: SCHOOL OF PUBLIC HEATH/DEPARTMENT OF PATHOLOGY/LKS FACULTY OF MEDICINE AND ELECTRON MICROSCOPE UNIT/UNIVERSITY OF HONG KONG
Omicron virus particles (orange) amass in vesicles and are released on the surface of Vero cells. A study suggests Omicron replicates less well deep inside human lungs.