New Scientist - USA (2020-10-24)

24 October 2020 | New Scientist | 23

A

S I write this, my 19-year-
old son is self-isolating in
his university room with
symptoms of covid-19, awaiting
test results. He is quite poorly,
though overwhelmingly likely to
make a full recovery. But I worry
that he will be one of the few
young adults who get seriously
ill or even die, or end up with
long-term health problems.
To some, however, his illness
is welcome; in fact, they wish it
on all of his peers. According to
the signatories of an open letter
called the Great Barrington
Declaration, lockdown measures
are doing more harm than good
and we should open up society
and let the virus rip.
OK, that is a bit of an
exaggeration. The declaration –
named after the US town where it
was signed – advocates a strategy
called “focused protection” under
which the most vulnerable people
shield and everybody else “should
immediately be allowed to resume
life as normal”. This will then
allow herd immunity to build up.
The declaration publicly
exposed a scientific disagreement
that has been simmering for
months. On one side are
mainstream scientists who
reluctantly see restrictions on
freedom as the only way to keep
a lid on the pandemic while we
wait for vaccines; on the other, the
libertarians who see the damage
done to economies and individual
lives as too high a price.
The mainstream media lapped
MIup the disagreement narrative,
CH
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Comment

Graham Lawton is a staff

writer at New Scientist

Views

The columnist

Annalee Newitz

asks why email

still exists p24

Aperture

A giant particle

hunter gets a

major upgrade p26

Letters

On balance:

life on two legs is

complicated p28

Culture

How big data won

an election for John

F. Kennedy p30

Culture columnist

Simon Ings finds

Black Box intriguing

yet melancholy p32

but completely missed the

fundamental problem with the

declaration: its extremely dubious

claims about herd immunity. This

is central to the strategy, but the

document badly fluffs the science.

Herd immunity is conceptually

simple. If enough people become

immune to an infectious agent,

the entire herd is protected

because infectious people rarely

encounter a non-immune person,

and so transmission fizzles out.

The level of individual

immunity required to attain

herd immunity against a virus

depends on how infectious it is,

as measured by R, the average

number of people that each

infectious person infects. The

classic example is measles, which

has an R number of around 15

and a herd immunity threshold

of 95 per cent. The numbers for

the coronavirus SARS-CoV-2 are

about 3.5 and 60 to 70 per cent.

Herd immunity has only ever

been attained by vaccination.

But the declaration advocates

naturally acquired immunity.

In other words, letting between

two-thirds and three-quarters of

the population catch the virus.

There are a number of issues

with this, not least collateral

damage. Even if the death rate is

under 1 per cent, letting the

virus run free will hospitalise

and kill millions.

But there is another crucial

scientific detail that the

declaration – along with most

discussions of herd immunity –

misses. We can’t take it for granted

that widespread individual

immunity will automatically

create herd immunity.

Herd immunity can only be

built if the immune response

totally prevents individuals from

picking up and transmitting the

virus. That sometimes happens,

but often doesn’t. A lot of the

time, an immune response stops

us from falling ill if we reacquire

the virus, but doesn’t prevent

onward transmission. The same

is true of vaccines.

We don’t yet know whether

natural immunity to SARS-CoV-2

(or the experimental vaccines)

will halt transmission. Until we

do, assuming that herd immunity

will automatically appear is

unscientific and, frankly,

irresponsible.

There are many other reasons

to be sceptical of the declaration.

It doesn’t even mention the

debilitating, lasting effects of

“long covid”, for example. But they

are of secondary significance to

the fundamental hole at its heart:

the mystifying and dangerous

failure to properly grasp the

concept of herd immunity.

Get well soon, son. ❚

Absurd about the herd

Assuming that herd immunity will result f rom letting most people

get covid-19 is unscientific and irresponsible, says Graham Lawton