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Supported by National Institute of General Medical Sciences grant
U54GM088558 (M.L.). We thank R. Kahn, S. Bellan, and A. Rid
for helpful conversations as we were writing this article, R. Kahn
for research assistance, and anonymous reviewers for written
comments. The content is solely the responsibility of the authors
and does not necessarily represent the official views of the
National Institute of General Medical Sciences or the National
Institutes of Health. M.L. served on the Scientific Advisory Group
for the Ebola ça Suffit vaccine efficacy trial (unpaid position) and
has received consulting fees or honoraria from Merck, Pfizer,
Antigen Discovery, and Affinivax. His research has received funding
(through his employer) from Pfizer and PATH Vaccine Solutions.
Discussions leading to the Oxford University Ethox workshop on
Ethical Design of Vaccine Trials in Emerging Infections helped
stimulate this paper.
When an emerging disease
Graham F. Medley* and Anna Vassall
Epidemics, such as HIV in the early 1980s and Ebola in 2014, inspire decisive government
investment and action, and individual and societal concern, sometimes bordering on panic.
By contrast, endemic diseases, such as HIV in 2017 and tuberculosis, struggle to maintain the
same attention. For many, the paradox is that endemic disease, in its totality, continues to
impose a far higher public health burden than epidemic disease. Overall, the swift political
response to epidemics has resulted in success. It has proven possible to eradicate epidemic
diseases, often without the availability of vaccines and other biomedical technologies. In recent
times, only HIV has made the transition from epidemic to endemic, but diseases that have
existed for centuries continue to cause most of the infectious disease burden.
Characterization of a disease as either epi- demic or endemic is commonly understood epidemiologically, but we argue that the so- cial framing of a disease as “epidemic” or “endemic” is equally important. For livestock, the relationship between disease phase and
social response is made more explicit: Diseases are
defined as “exotic,” and thence acquire a legal status requiring government action to eliminate
them. Other endemic or livestock “production
diseases” are permitted to remain endemic (1).
By contrast, in human health, disease status and
responses are rarely legally determined. As with
animal diseases, human diseases acquire a social
status, primarily based on their perceived risk,
that determines their acceptability and the level
of intervention deemed appropriate. In this exploration of the characteristics of epidemic and
endemic infectious disease, we highlight the pivotal role of risk and risk perception in explaining
individual and societal responses to diseases in
different phases of their establishment in populations. The heterogeneity of risk across populations is one of the key aspects we consider. We
argue that individual and societal risks both determine, and are determined by, the classification
of a disease as epidemic or endemic. Thus, the
classification of disease reflects both biological
and social phenomena.
The public response
Responses to epidemics tend to be public, seem-
ingly without resource constraints, and often com-
bine the efforts of national and global public
health institutions. For example, HIV provoked
over a 10-fold increase in development funding
for health in a decade and the formation of new
public institutions such as the Joint United Na-
tions Programme on HIV/AIDS (UNAIDS) (2). As
diseases become endemic, they become increas-
ingly tolerated, and the locus of responsibility may
shift to the individual. Rather than public au-
thorities actively detecting cases and subsidizing
risk protection, people may be increasingly en-
couraged to pay for the means to manage their
own risk and seek care. Likewise, the focus of any
global response may move away from direct pro-
vision of services by international agencies to
other forms of intervention, such as building na-
tional capacity more generally, supported by do-
mestic financing (3).
For many, the primacy of the national and
global response to epidemics appears to be an
“overreaction,” as resources are pulled in across
government departments to rapidly control and
limit the outbreak. Responses may thus be perceived as a detriment to other health priorities,
such as routine vaccination. Epidemics may provoke broad multisectoral responses led by the political executive, mass-information campaigns,
and military mobilization. Epidemics may also
prompt substantial public investment in vaccines or the development of treatments: The UK
government is estimated to have spent 1.2 billion
pounds sterling on the swine flu epidemic (4), and
licensing arrangements for diagnostics, medicines,
and vaccines in emergencies are relaxed (5). The
rationale for the political imperative is twofold.
First, epidemics can most (cost)-effectively be controlled when the number of cases is very small,
and thus, even an ill-informed rapid response may
be more beneficial and efficient than a cautious
informed one (6). Second, there is a (often highly
uncertain) risk of catastrophic impact: Epidemics
have destroyed civilizations. Politicians therefore
need to weigh investment against highly uncertain, but potentially devastating, social, health,
and economic consequences. The “public health
paradox” ensures that if the epidemic is successfully controlled, then it is highly likely that the
eventual impact of the epidemic disease will have
been less than the opportunity cost of the resources allocated to it from other health areas.
The experience of 1918 still serves to remind us
that, had we not responded to H1N1 as we did, it
could have been much, much worse.
At some point, the sociopolitical response to
an emerging disease starts to change. Investment
in the disease may become institutionalized in
Department of Global Health and Development, London
School of Hygiene and Tropical Medicine, WC1E 7HT
*Corresponding author. Email: email@example.com
EMERGING INFECTIOUS DISEASES