The Economist - USA (2020-11-28)

70 Science & technology The EconomistNovember 28th 2020

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more information about the nature of the

immune response in the weeks ahead.

As with data on the other two vaccines,

much of the information provided so far is

frustratingly preliminary. However, the

Oxford group say they hope soon to submit

a paper, presumably containing fuller in-

formation, to a journal. It is not clear when

those developing the other two vaccines

will do the same, but data from their trials

will be made available prior to meetings

with the American regulator in December.

Haste versus speed

The headline figure of 70% efficacy con-

trasts superficially with announced values

of 95% for the other two vaccines. But,

tempting as it is to compare these figures,

that is actually hard to do. The most impor-

tant reason for this is that developers count

covid-19 cases in different ways. In particu-

lar, the AstraZeneca-Oxford trials checked

participants for asymptomatic infection,

rather than relying on self-reported symp-

toms to establish who was infected. The

number of cases after vaccination may

therefore seem higher than for the Pfizer-

BioNTech and Moderna jabs, which relied

on self-reporting by patients with a fol-

low-up confirmatory test.

One bonus of the AstraZeneca-Oxford

offering is that, if approved, it could be

rolled out quickly. Pascal Soriot, AstraZe-

neca’s boss, says his firm has partnerships

with suppliers in India, Latin America,

Russia and Thailand. The Serum Institute

in India agreed to manufacture the vaccine

in bulk as long ago as April. “We are going

to supply low- and middle-income coun-

tries around the world from different

sources,” Mr Soriot says. “We are aiming at

doing this more or less at the same time, so

everybody gets access in an equitable man-

ner as quickly as possible.” Altogether, As-

traZeneca says the capacity exists to make

3bn doses of its vaccine over the course of

next year. That compares with 1.3bn of the

Pfizer-BioNTech vaccine, while Moderna

hopes for between 500m and 1bn.

The AstraZeneca-Oxford vaccine is also

cheap, and can be kept for at least six

months in a normal refrigerator, meaning

it can be stored in any surgery or pharmacy

around the world. Moderna’s vaccine, by

contrast, can be kept in an ordinary fridge

for just a month. The Pfizer-BioNTech of-

fering is even more sensitive. For most of

the time it needs ultra-cold storage at

-70°C. It can sit in a standard fridge for only

a few days. Richard Hatchett, the head of

cepi, a foundation that pays for research

into vaccines against novel pathogens,

says he thinks the AstraZeneca-Oxford vac-

cine has the potential to alter the course of

the pandemic, and could be delivered any-

where, including poor countries.

Although AstraZeneca says its vaccine

was well tolerated by those who received it,

questionsremainaboutanunknownad-

verseeventwhichcausedtrialstobehalted

temporarilyearlierthis year.These, and

othermatters,mustnowbeconsideredby

regulators,astheyassessapplicationsfor

emergencyauthorisationthatthemakers

of allthreevaccines willsubmit.Astra-

Zenecasaysitwillalsoseekanemergency

listingfromtheWorldHealthOrganisa-

tion.Thatwouldpermititsjabstobeused

inplaceswhichdonothaveregulatoryau-

thoritiescapableofassessingvaccines.

If timewerenotoftheessence,it would

makesensetowaitforlonger-termdataon

allthenewvaccines.Butinthefaceofa

pandemic,thatisnotsensible.Regulations

toallowforemergencyusearedesignedfor

justsuchsituations.Regulatorswill,how-

ever,havetokeeptightcontrolofthese

newvaccinestostartwith.Attheoutset

their use will probably be restricted to

thosewhoneedthemmost—doctors,nur-

sesandotherhealth-careworkers,andalso

theelderly.Regulatorswillalsoinsiston

closemonitoringforside-effects.But,as

dataaccumulateoverthefirstmonthsof

nextyear,thosechainsarelikelytobeloos-

ened. The pastthree weeks, then, have

transformedtheprospects for2021. The

worldnowknowscovidvaccinesarepossi-

ble.Letthehardworkbegin. 7

I

n the history of medicine, praise is

rightly showered on those who invented

vaccines, antibiotics, antiseptics and an-

aesthetics. Few, though, remember Charles

Chamberland, inventor of the humble

autoclave. Yet the ability to sterilise surgi-

cal instruments reliably, by exposing them

to high-pressure steam in such a device,

has been crucial to the development of

modern surgery. A mere 12 minutes in an

autoclave at 121°C and two atmospheres of

pressure kills 99.99% of common patho-

genic bacteria. Standard boiling, at 100°C

and one atmosphere, takes 80 hours to

achieve that level of bactericide.

Electrically powered autoclaves have, as

a consequence, become so routine as to be

almost unregarded—at least in those

places with a reliable electricity supply.

Where electricity is not reliable, though, it

can be hard to keep surgical instruments

germfree. This is a problem to which Zhao

Lin of the Massachusetts Institute of Tech-

nology thinks he may have an answer. As

he and his colleagues describe in Joule, they

have designed an autoclave that is powered

directly by sunlight. And not only that;

they also reckon it should cost just a tenth

as much to make commercially as a con-

ventional autoclave of equivalent potency.

Dr Zhao’s device is a work of simplicity

and cheap materials. It consists of a metre-

long box of rectangular cross section, with

two curved fins of polished aluminium,

just under 30cm high, sticking out of the

top (see diagram). Each fin, seen end on,

forms a section of a parabola, and it is a

property of parabolic mirrors to focus light

from distant sources (the sun, for example)

onto a single point—or, in the case of elon-

gated mirrors like these, onto a line.

The new invention’s principal trick is

that these focal lines coincide with the

edges of a copper plate within the box. This

plate is part of a commercially available de-

vice called a fin-tube absorber. The absorb-

er’s other element is a copper pipe running

along the plate’s central axis. The particular

geometry of the aluminium fins means

that any incident sunlight will continue to

be focused onto the copper plate even

when the sun is not directly overhead. Any-

thing inside the pipe is therefore going to

get—and stay—pretty hot.

Within the box, the fin-tube absorber is

seated on a bed of glass fibre, an excellent

insulator, and it is covered with a layer of

silica aerogel. This stuff, referred to collo-

quially as “solid smoke” because it has a

density of a mere 200 milligrams per cubic

centimetre, has the valuable properties of

being transparent to light but opaque to

heat. This means it admits the sunshine re-

flected from the mirrors while keeping the

pipe as hot as possible. Although such a

material sounds rather high-tech, and

does, indeed, require specialist equipment

to make, silica aerogel is actually quite

cheap to buy, at $4 a litre. And a production

model of the autoclave, Dr Zhao reckons,

would require only half a litre of the stuff.

The whole thing is then topped off with

a pane of glass, to protect the aerogel from

And now it can be used indirectly for

that purpose, too

Sterilising medical instruments

Sunlight is the best

disinfectant

Reflectedglory

Source: “A passive high-temperaturehigh-pressure solar steam

generator for medical sterilisation”, Zhao et al., Joule (2020)

A solar-poweredautoclave

↙ Aluminium mirrors ↘

Box

Insulation

Glass

Incident

light

Focus

Aerogel

Fin-tube

absorber