66 Science & technology The EconomistAugust 22nd 2020
2 cians say that the share of covid-19 patients
with lingering problems is far higher than
is seen with other viral illnesses such as in-
fluenza. The problems are also more va-
ried, often including lung, heart and psy-
chological symptoms, says Sally Singh of
the University of Leicester, who leads the
development of a covid-19 rehabilitation
programme for Britain’s health service.The walking wounded
Anecdotal reports of long-lasting illness
have been around since the early days of
the pandemic. But with more than 22m
cases confirmed worldwide, and with in-
fection rates having peaked several months
ago in most rich countries, statistical pat-
terns about the virus’s lingering effects are
starting to emerge. A paper in the British
Medical Journalon August 11th concluded
that as many as 60,000 people in Britain
have long-term symptoms. Yet only about
6% of Britain’s population—around 4m
people—seems to have been infected with
the virus so far.
Severity of the illness is one predictor of
lasting problems. Ian Hall, the director of
the Biomedical Research Centre at the Uni-
versity of Nottingham, reckons that
30-50% of patients hospitalised with co-
vid-19 have significant symptoms six to
eight weeks after they have been dis-
charged. That number rises further for pa-
tients who were admitted to an icu. But
even those who escaped with a mild ill-
ness, like Laura, are at risk. More than 10%
of them remain unwell for more than three
weeks, according to a patient-tracking
study that follows mostly American and
British patients. They struggle with fatigue,
breathlessness, body aches and cognitive
problems which many describe as “brain
fog” (see chart 2).
Some long-term covid-19 patients may
be suffering from undiagnosed conditions
such as diabetes or thyroid dysfunction,
which are “unmasked” by the infection,
says Avindra Nath of the National Insti-
tutes of Health in America. For others, the
collection of symptoms is suggestivelysimilar to those seen in chronic fatigue
syndrome (cfs). The biological causes of
cfsare still poorly understood, but data
from America indicate that three-quarters
of cases follow viral or bacterial infections.
One hypothesis is that the syndrome is
caused by the immune system failing to
properly stand down after being called on
to battle an infection. It may be that sars-
cov2, the virus that causes covid-19, is
unusually likely to provoke such a linger-
ing over-reaction.
If the root cause is not known, then the
growing understanding of just what co-
vid-19 can do to the body can at least sug-
gest what sorts of care long-term sufferers
may need. The hallmark of many covid-19
cases is damage to the lungs. Aggressive in-
flammation leads to the destruction of
lung tissue and the formation of scars. The
scarring, in turn, impedes the flow of oxy-
gen from the lungs into the blood. That can
cause breathlessness, even with light exer-
cise. Small studies of covid-19 patients dis-
charged from hospitals have found that
25-30% have impaired oxygen flow.
The prognosis is unclear. People treated
in icus for other viral infections usually re-
cover about 80% of their previous lung
function fairly quickly, but the final 20%
can take three to six months, says Dr Hall.
And in some cases lung scarring can wors-
en over time, especially if combined with
new health problems later in life.
Breathing problems can also arise from
another effect of covid-19—its tendency to
cause blood clots, which is unusual for a
respiratory virus. When they form in the
lungs, clots can choke off blood flow, mak-
ing it even harder to absorb oxygen. And
the virus may cause breathlessness in a
more subtle way, too, by damaging the lin-
ing of blood vessels, which limits how
much blood can flow through them.
Covid-19 can also damage the heart. It
can inflame the tissues that surround the
organ, as well as the blood vessels that ferry
nutrients to it. That can weaken the heart
muscle, and eventually lead to heart fail-
ure. Blood clots cause problems here, aswell, since the heart must pump harder to
push blood through partly blocked vessels.
Over time, that can weaken the muscle.
Nobody knows exactly how often such
cardiac complications occur. But news
from Germany is worrying, says Clyde
Yancy, a cardiologist at Northwestern Uni-
versity, in Illinois. Using mriscans, one
study found evidence that covid-19 causes
inflammation and other heart changes—
including in people who had tested posi-
tive for the virus more than two months
earlier and were, by the time of their scans,
free from symptoms. The changes were
small, and not enough by themselves to
cause clinical symptoms. But even a minor
injury to the heart may eventually lead to
heart failure if it lingers for long enough,
says Dr Yancy.
Least understood are the long-term ef-
fects of covid-19 on the nervous system and
the brain. Patients with lingering post-co-
vid symptoms complain of headaches, tin-
gling and numbness in the feet, and other
neurological problems. Problems that sug-
gest a dysfunction of the autonomic ner-
vous system, such as irregular heart beat,
dry mouth and gastrointestinal problems
are also common, says Dr Nath. But the ex-
act cause of such symptoms remains un-
clear, as does the reason why more than
half of those infected suffer a temporary
loss of their sense of smell. (Some, rather
than losing it, have it altered instead, so
that things smell different after the infec-
tion than they did beforehand.)
Confronted with a baffling array of
symptoms and few detailed explanations
about exactly what is going wrong, doctors
are desperate for guidance. A third of gen-
eral practitioners in Britain already have
patients with lasting post-covid symp-
toms. For now, the best they can offer is re-
ferral to lung or cardiac rehabilitation.
Such therapy may improve a patient’s qual-
ity of life with something as simple as a
breathing exercise. Britain, Belgium and
other countries are setting up specialised
covid-19 rehabilitation programmes for
those recovering from the disease. Waiting
lists are already long.
In the absence of understanding, doc-
tors must fall back on lessons from other
illnesses. Lingering symptoms are not the
exclusive preserve of covid-19. Full recov-
ery from other viral diseases such as influ-
enza can occasionally take months. Data
on cfssuggests chances of recovery are
best in the first three months.
More specific data are on the way. Stud-
ies in America, Britain, China and Europe
have enrolled thousands of patients, and
should begin reporting initial results in the
next few months. But for now, those suffer-
ing the lingering effects of the disease must
deal not only with the physical symptoms,
but with uncertainty about just how long it
will take them to get better. 7ThelongroadtorecoverySources:CentresforDiseaseControlandPrevention;CovidSymptomsStudy2ConfusionChestpainShortnessofbreathLossoftaste/smellHeadacheCoughFatigue806040200Prevalenceofsymptomsincovid-19patients,%
Mostcommonpersistentsymptoms
At positive test 14-21dayslater86420
3835302520151052Duration of covid-19symptoms
% of patientsDays