The EconomistNovember 21st 2020 Science & technology 752 will save lives in groups of people who have
been hit disproportionately hard by co-
vid-19. Data published this week in the Lan-
cetsuggest that the elderly respond well to
the AstraZeneca vaccine, too. Continuing
reviews of the safety of these vaccines sug-
gest they are well tolerated, although a mi-
nority do get a day of flu-like symptoms,
such as fatigue, muscle and joint pain.
The first two vaccines both look like
worthy weapons in the fight against co-
vid-19. There is, though, one thing about
the Moderna vaccine that sets it apart. It
can be kept in a regular fridge at between
2°C and 8°C for 30 days. The Pfizer vaccine,
by contrast, needs to be kept ultracold, at
-70°C or below, most of the time. That will
make the Moderna vaccine far easier and
cheaper to distribute (although the cost of
the Moderna vaccine itself is higher). If the
AstraZeneca vaccine proves successful, it,
too, is thought likely to need only a stan-
dard refrigerator to preserve it. And be-
cause this vaccine is also a fraction of the
price of the others, it might still end up be-
ing the most popular choice.
All three vaccines use the same strategy:
to introduce into the human body rna(a
molecule similar to dna) that carries the
recipe for “spike”, a protein abundant on
the outsides of particles of sars-cov-2, the
virus that causes covid-19. The body then
uses this recipe to manufacture spike, and
the immune system, recognising the pro-
tein as alien, mounts a response to it. Thus
stimulated, the immune system can react
rapidly if it subsequently encounters the
spike proteins of actual viruses.
The vaccines from Pfizer and Moderna
introduce the rnadirectly, as molecules
known as messenger rna(mrna) held in-
side small, fatty particles called liposomes.
AstraZeneca’s offering instead incorpo-
rates the rnainto the genetic material of a
harmless cold virus. The mrnaapproach is
regarded as particularly interesting, be-
cause this is the first successful example of
what researchers hope will be a new class
of drugs that work by feeding cells instruc-
tions to make therapeutic proteins in situ.
Message received
Learning how to introduce mrnainto the
body without it either being destroyed or
stimulating an unhelpful immune re-
sponse has been challenging. These two
new vaccines are the first evidence of the
technology’s potential. Moderna is pursu-
ing mrnaas the basis for other vaccines,
against such pathogens as cytomegalo-
virus, influenza, paediatric-respiratory-
syncytial virus and Zika. BioNTech, mean-
while, isexploringthe useof mrnatostimulate the immune system to fight can-
cer. Its pipeline includes treatments for
malignant melanoma and for prostate,
head-and-neck and breast cancers.
As for covid-19, the success of these rap-
idly created mrnavaccines bodes well for
dealing with any future mutations of sars-
cov-2. As the pandemic continues to
spread, and such mutations accrue, it is
possible that the excellent responses these
vaccines now provoke could wane. That,though, should not be a problem. Just as
natural selection can tinker with the virus’s
genetic code, so too can scientists tinker
with the code in the vaccines. And, once
they have proved themselves, those vac-
cines could be adjusted every year, as hap-
pens already with influenza vaccines. The
tools the world needs to emerge from the
covid-19 pandemic are starting to arrive.
That they are all arriving at the same time is
an unlooked-for blessing. 7L
ake baikal, near Russia’s border with
Mongolia, is, by volume, the biggest
body of fresh water on Earth. At 1.6km, it
is also the deepest. Several unusual
animals call it home, including the
world’s only species of freshwater seal.
Baikal’s seals are abundant. There are
about 100,000 of them. But the lake is
nutrient-poor, so how they do so well has
been a mystery. A study just published in
the Proceedings of the National Academy of
Sciences, by Watanabe Yuuki of the Na-
tional Institute of Polar Research, in
Tokyo, suggests the answer is by filtering
tiny organisms from the water.
Most seals eat fish. And Baikal seals
do, indeed, have needle-pointed canines
of the sort expected of piscivores. But in
1982 researchers noted that they sport a
second sort of specialised tooth behind
those canines. These have frilled cusps
which resemble combs. At the time,
nobody knew what to make of them. But
Dr Watanabe speculated that they might
be an adaptation for feeding on other
strange creatures dwelling in the lake.
Seals arrived in Baikal 2m years ago,
from the Arctic Ocean. So too did some
much smaller marine creatures, knownasamphipods.Thesehavediversified
into more than 340 indigenous species.
One of them, Macrohectopus branickii,
spends its days hiding in the depths of
the lake and then forages in the shallows
at night in great numbers.
Marine mammals the size of seals
would normally see amphipods as too
small to hunt. But Dr Watanabe won-
dered if the Baikal seals’ comblike teeth
might have evolved to enable them to
rake these tiny crustaceans from the
water in sufficient quantities to make
them useful prey—much as some whales
collect krill using comblike structures
called baleen plates. He and his col-
leagues therefore attached waterproof
video cameras and accelerometers to a
few seals, to monitor what they were
getting up to. This equipment remained
attached to the animals for between two
and four days, before coming loose and
floating to the lake’s surface, whence the
researchers were able to recover it.
Footage from the cameras and data
from the accelerometers showed that the
seals were indeed pursuing the dense
amphipod aggregations that form at
night. They would dive in with their
mouths open and collect prey before
making another pass. Dr Watanabe esti-
mates that each seal captures an average
of 57 amphipods per dive—and thus
thousands of them a day. The needlelike
canines are not redundant, for the seals
do hunt fish as well. But they also com-
pete with those fish for the amphipods,
thus partially bypassing a link in the food
chain and perhaps thereby maintaining
themselves in larger numbers than
would otherwise be possible.
Whether, were some of these filter-
feeding seals to make it back to the
ocean, they would follow the baleen-
whale path and evolve into giants, is an
interesting speculation. But even con-
fined to their lake, Baikal seals provide an
intriguing example of parallel evolution.Cutting out the middle man
EvolutionSieve-toothed seals may be whales in the makingCorrection. In last week’s Briefing (“Covid-19
vaccines”, November 14th), we said in the table
called “A full field” that the candidate from Novavax
is an “inactivated” vaccine. It is actually a “protein-
subunit” vaccine. Sorry.