177-B 9 JULY 2021 • VOL 373 ISSUE 6551 sciencemag.org SCIENCERESEARCHCORONAVIRUS
Focusing on
transmission risk
Stopping downstream trans-
mission is an important aspect
of mitigating the COVID-19
pandemic. Much of the modeling
used to understand transmission
patterns assumes that every-
one has the same risk but this
is not the case. Heterogeneity
in exposure related to occupa-
tion, housing, and economic
circumstances can substantially
affect the risk of being infected
and of infecting others. In a
Perspective, Cevik and Baral
discuss the factors that drive
transmission of severe acute
respiratory syndrome corona-
virus 2 and argue that people
with the highest risk, such as
those in economically deprived
neighborhoods, those living in
large households, and those who
cannot work from home, should
receive targeted support to allow
them to decrease contacts and
thus break transmission chains.
Without such support, these
communities are left at higher
risk of infection, death, and eco-
nomic hardship. —GKA
Science, abg0842, this issue p. 162LIGHT-MATTER COUPLING
Captivating cavities
Laser technology is a famil-
iar example of how confining
light between two mirrors can
tune its properties. Quantum
mechanics also dictates that
even without extraneous light,
matter confined in a cavity
resonant with its electronic
or vibrational transitions can
couple with vacuum electro-
magnetic field fluctuations.
Garcia-Vidal et al. review the
remarkable and still somewhat
mysterious implications of this
“strong-coupling” regime, with
manifestations ranging from
enhanced charge transport to
site-selective chemical reactiv-
ity across a range of molecular
and solid-state materials. —JSY
Science, abd0336, this issue p. 178CORONAVIRUS
Correlates of
infectiousness
The role that individuals with
asymptomatic or mildly symp-
tomatic severe acute respiratory
syndrome coronavirus 2 have
in transmission of the virus is
not well understood. Jones et al.
investigated viral load in patients,
comparing those showing few,
if any, symptoms with hospi-
talized cases. Approximately
400,000 individuals, mostly
from Berlin, were tested from
February 2020 to March 2021
and about 6% tested positive.
Of the 25,381 positive subjects,
about 8% showed very high viral
loads. People became infectious
within 2 days of infection, and in
hospitalized individuals, about
4 days elapsed from the start
of virus shedding to the time of
peak viral load, which occurred
1 to 3 days before the onset of
symptoms. Overall, viral load
was highly variable, but was
about 10-fold higher in persons
infected with the B.1.1.7 variant.
Children had slightly lower viral
loads than adults, although this
difference may not be clinically
significant. —CA
Science, abi5273, this issue p. 180MICROBIOMES
Baboons inform on
human gut microbiota
Commensal bacteria are found
throughout an organism, but it is
not known whether associations
between gut bacteria and their
host are heritable. Grieneisen
et al. examined changes in
the microbiomes of 585 wild
baboons from fecal samples
collected over 14 years (see the
Perspective by Cortes-Ortiz and
Amato). Almost all microbiome
traits tested demonstrated some
level of statistically significant
heritability. Most heritability
values were low but varied over
time correlating with the age
of the host. Baboons live in an
environment similar to thatpostulated for early humans and
have a microbiome similar to that
of humans. Thus, this heritability
of the microbiome may reflect
similar genetic determinants in
humans, for which similar data-
sets are not available. —LMZ
Science, aba5483, this issue p. 181;
see also abj5287, p. 159ICE PHYSICS
Ice goes bendy
One well known characteristic
of ice is that it fractures instead
of bending when strained. This
characteristic is caused by the
inevitable defects introduced
into the ice structure during
solidification. Xu et al. show that
very thin, carefully grown ice
microfibers can bend a lot, up
to about 11%, and still remain
elastic (see the Perspective by
Schulson). This value is reason-
ably close to theoretical limits
previously estimated. The fibers
are also super clear, allowing for
efficient light transmission. —BG
Science, abh3754, this issue p. 187;
see also abj4441, p. 158CANCER
Down with leukemia
Down syndrome is a congenital
disorder caused by the trisomy of
chromosome 21, and it is associ-
ated with a greatly increased risk
of leukemia with origins in fetal
development. Infants with Down
syndrome are often born with
a preleukemic condition, which
later resolves in most cases. By
using gene-edited human cells
implanted into mouse models,
Wagenblast et al. recapitulated
the development of preleukemia
and leukemia in the context
of Down syndrome (see the
Perspective by Roberts and Vyas).
A specific mutation triggered
a preleukemic condition in the
context of trisomy 21 as expected,
but progression to full-blown leu-
kemia required a different genetic
path and was not dependent on
trisomy 21. —YN
Science, abf6202, this issue p. 179;
see also abj3957, p. 155SUPERCONDUCTIVITY
Looking for
magnetic clues
Thin films of the neodymium
nickelate NdNiO 2 doped with
strontium have recently been
found to be superconduct-
ing. This materials class bears
structural and electronic
similarities to the famed cuprate
superconductors, but how
far the analogy goes remains
unclear. Lu et al. used resonant
inelastic x-ray scattering to look
for magnetism, which exists in
the cuprates, in Nd1-xSrxNiO 2
films (see the Perspective
by Benckiser). The authors
observed magnetic modes in the
undoped compound that had a
doping evolution consistent with
the behavior of a doped Mott
insulator. —JS
Science, abd7726, this issue p. 213;
see also abi6855, p. 157SENSORY EVOLUTION
From savory to sweet
Seeing a bird eat nectar from
a flower is a common sight in
our world. The ability to detect
sugars, however, is not ancestral
in the bird lineage, where most
species were carnivorous. Toda
et al. looked at receptors within
the largest group of birds, the
passerines or songbirds, and
found that the emergence of
sweet detection involved a single
shift in a receptor for umami
(see the Perspective by Barker).
This ancient change facilitated
sugar detection not just in nectar
feeding birds, but also across
the songbird group, and in a way
that was different from, though
convergent with, that in hum-
mingbirds. —SNV
Science, abf6505, this issue p. 226;
see also abj6746, p. 154ANTIVIRAL DEFENSE
An antiviral Dicer defends
stem cells
Stem cells have a pivotal role in
maintaining tissue architecture,Edited by Michael FunkALSO IN SCIENCE JOURNALS
0709eISIO.indd 177-B 7/2/21 5:51 PM