The WHO Scientific and Technical Advisory Group for Infectious Hazards (STAG-IH),
working with the WHO secretariat, reviewed available information about the outbreaks
of 2019 novel coronavirus disease (COVID-19) on Feb 7, 2020, in Geneva, Switzerland,
and concluded that the continuing strategy of containment for elimination should continue,
and that the coming 2–3 weeks through to the end of February, 2020, will be crucial
to monitor the situation of community transmission to update WHO public health recommendations
if required.
Genetic analysis early in the outbreak of COVID-19 in China revealed that the virus
was similar to, but distinct from, severe acute respiratory syndrome coronavirus (SARS-CoV),
but the closest genetic similarity was found in a coronavirus that had been isolated
from bats.
1
As there was in early January, 2020, scarce information available about the outbreak,
knowledge from outbreaks caused by the SARS-CoV and Middle East respiratory syndrome
coronavirus (MERS-CoV) formed the basis for WHO public health recommendations in mid-January.
2
However, the availability of more evidence in the past month has shown major differences
between the outbreaks and characteristics of COVID-19 compared with those of SARS-CoV.
Recognising the Wuhan-focused and nationwide outbreak responses in China, WHO has
encouraged countries with heavy air travel exchange with Wuhan to take precautionary
public health measures
2
and, if there is imported infection, to undertake activities that could lead to the
elimination of the virus in human populations as occurred during the 2003 SARS outbreak.
3
After the SARS outbreak, a few follow-on outbreaks occurred, including accidents in
laboratories researching SARS-CoV.
4
SARS-CoV is thought to have been eliminated from human populations during 2003, and
there have been no reports in the medical literature about SARS-CoV circulation in
human populations since then.
The 2003 SARS outbreaks are thought to have originated from the spillover of a mutated
coronavirus from animals sold in a live animal market in Guangdong province in China
to a few humans, and it then surfaced as a large cluster of pneumonia in health-care
settings in Guangdong province.
5
Although the causative agent was then unknown, an infected medical doctor who had
been treating patients in Guangdong province travelled to Hong Kong when he became
ill and became an index case for hospital-associated and community outbreaks in Hong
Kong and in three countries outside of China. The causative agent was later identified
as a coronavirus and named SARS-CoV. The SARS outbreaks were at times characterised
by several superspreading events—eg, hotel-based transmission from one infected hotel
guest to others who travelled to Canada, Singapore, and Vietnam.
6
One large apartment complex-based outbreak of SARS was later found to be caused by
aerosolisation of virus contaminated sewage.
6
COVID-19 is thought to have been introduced to human populations from the animal kingdom
in November or December, 2019, as suggested by the phylogeny of genomic sequences
obtained from early cases.
7
The genetic epidemiology suggests that from the beginning of December, 2019, when
the first cases were retrospectively traced in Wuhan, the spread of infection has
been almost entirely driven by human-to-human transmission, not the result of continued
spillover. There was massive transmission in a matter of weeks in Wuhan, and people
in the resulting chains of transmission spread infection by national and international
travel during the Chinese New Year holidays.
COVID-19 seems to have different epidemiological characteristics from SARS-CoV. COVID-19
replicates efficiently in the upper respiratory tract and appears to cause less abrupt
onset of symptoms, similar to conventional human coronaviruses that are a major cause
of common colds in the winter season.
8
Infected individuals produce a large quantity of virus in the upper respiratory tract
during a prodrome period, are mobile, and carry on usual activities, contributing
to the spread of infection. By contrast, transmission of SARS-CoV did not readily
occur during the prodromal period when those infected were mildly ill, and most transmission
is thought to have occurred when infected individuals presented with severe illness,
thus possibly making it easier to contain the outbreaks SARS-CoV caused, unlike the
current outbreaks with COVID-19.
6
© 2020 Kyodo News/Contributor/Getty Images
2020
Since January 2020 Elsevier has created a COVID-19 resource centre with free information
in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre
is hosted on Elsevier Connect, the company's public news and information website.
Elsevier hereby grants permission to make all its COVID-19-related research that is
available on the COVID-19 resource centre - including this research content - immediately
available in PubMed Central and other publicly funded repositories, such as the WHO
COVID database with rights for unrestricted research re-use and analyses in any form
or by any means with acknowledgement of the original source. These permissions are
granted for free by Elsevier for as long as the COVID-19 resource centre remains active.
COVID-19 also has affinity for cells in the lower respiratory tract and can replicate
there, causing radiological evidence of lower respiratory tract lesions in patients
who do not present with clinical pneumonia.
8
There seem to be three major patterns of the clinical course of infection: mild illness
with upper respiratory tract presenting symptoms; non-life-threatening pneumonia;
and severe pneumonia with acute respiratory distress syndrome (ARDS) that begins with
mild symptoms for 7–8 days and then progresses to rapid deterioration and ARDS requiring
advanced life support (WHO EDCARN clinical telephone conference on COVID-19, personal
communication with Myoung-don Oh [Seoul National University Hospital] and Yinzhong
Shen [Shanghai Public Health Clinical Center])
The case fatality ratio with COVID-19 has been difficult to estimate. The initial
case definition in China included pneumonia but was recently adjusted to include people
with milder clinical presentation and the current estimate is thought to be about
1–2%, which is lower than that for SARS (10%).
9
The actual case fatality ratio of infection with COVID-19 will eventually be based
on all clinical illness and at the time of writing information on subclinical infection
is not available and awaits the development of serological tests and serosurveys.
Presently COVID-19 seems to spread from person to person by the same mechanism as
other common cold or influenza viruses—ie, face to face contact with a sneeze or cough,
or from contact with secretions of people who are infected. The role of faecal–oral
transmission is yet to be determined in COVID-19 but was found to occur during the
SARS outbreak.
10
The lock-down of Wuhan City seems to have slowed international spread of COVID-19;
however, the effect is expected to be short-lived (WHO modelling group). Efforts are
currently underway in China, in the 24 countries to which infected persons have travelled,
and in public conveyances, such as cruise ships, to interrupt transmission of all
existing and potential chains of transmission, with elimination of COVID-19 in human
populations as the final goal. This WHO-recommended strategy is regularly assessed
each week by STAG-IH on the basis of daily risk assessments by WHO as information
becomes available from outbreak sites.
A plausible scenario based on the available evidence now is that the newly identified
COVID-19 is causing, like seasonal influenza, mild and self-limiting disease in most
people who are infected, with severe disease more likely among older people or those
with comorbidities, such as diabetes, pulmonary disease, and other chronic conditions.
Health workers and carers are at high risk of infection, and health-care-associated
amplification of transmission is of concern as is always the case for emerging infections.
People in long-term care facilities are also at risk of severe health consequences
if they become infected.
Non-pharmaceutical interventions remain central for management of COVID-19 because
there are no licensed vaccines or coronavirus antivirals. If the situation changes
towards much wider community transmission with multiple international foci, the WHO
strategy of containment for elimination could need to be adjusted to include mitigation
strategies combined with the following activities currently recommended by STAG-IH
on the WHO website.
First, close monitoring is needed of changes in epidemiology and of the effectiveness
of public health strategies and their social acceptance.
Second, continued evolution is needed of enhanced communication strategies that provide
general populations and vulnerable populations most at risk with actionable information
for self-protection, including identification of symptoms, and clear guidance for
treatment seeking.
Third, continued intensive source control is needed in the epicentre in China—ie,
isolation of patients and persons testing positive for COVID-19, contact tracing and
health monitoring, strict health facility infection prevention and control, and use
of other active public health control interventions with continued active surveillance
and containment activities at all other sites where outbreaks are occurring in China.
Fourth, continued containment activities are needed around sites outside China where
there are infected people and transmission among contacts, with intensive study to
provide information on transmissibility, means of transmission, and natural history
of infection, with regular reporting to WHO and sharing of data.
Fifth, intensified active surveillance is needed for possible infections in all countries
using the WHO-recommended surveillance case definition.
11
Sixth, preparation for resilience of health systems in all countries is needed, as
is done at the time of seasonal influenza, anticipating severe infections and course
of disease in older people and other populations identified to be at risk of severe
disease.
Seventh, if widespread community transmission is established, there should then be
consideration of a transition to include mitigation activities, especially if contact
tracing becomes ineffective or overwhelming and an inefficient use of resources. Examples
of mitigation activities include cancelling public gatherings, school closure, remote
working, home isolation, observation of the health of symptomatic individuals supported
by telephone or online health consultation, and provision of essential life support
such as oxygen supplies, mechanical ventilators and extracorporeal membrane oxygenation
(ECMO) equipment.
Eighth, serological tests need to be developed that can estimate current and previous
infections in general populations.
Finally, continued research is important to understand the source of the outbreak
by study of animals and animal handlers in markets to provide evidence necessary for
prevention of future coronavirus outbreaks.