a downgraded for indirectness because the studies used
SARS data, which does not reflect the presymptomatic infectiousness of
COVID-19
b Only 2 cases of SARS out of >95,000
quarantined
Abbreviations: COVID-19: coronavirus disease 2019; NA: not applicable;
SARS: severe acute respiratory syndrome
3.2.2 Resource use and comparative effectiveness of quarantine
We did not identify any studies assessing resource use of quarantine for
travelers from regions with high transmission rates, nor on comparative
effectiveness of diverse types of quarantine.
4 Discussion
To the best of our knowledge, this is the first systematic evidence
synthesis on the effectiveness of quarantine for COVID-19 using
additional data from other severe coronavirus outbreaks. The
evidencebase is very limited because 19 of the 21 included studies are
on SARS and MERS while only two are on SARS-CoV-2. Nevertheless,
included studies consistently report a benefit of quarantine measures.
Quarantine of people exposed to confirmed cases resulted in higher
numbers of infections and deaths averted than through quarantine of
those who repatriated from regions with an outbreak. In 2011, Jefferson
et al. conducted a systematic review on physical interventions to combat
respiratory diseases in general. They did not find valid evidence on the
effectiveness of quarantine and stressed the need for further
research.47
The searches identified only two modeling studies on prevention and
control measures for the current COVID-19
outbreak.45,46 Both studies concluded that prevention
and control measures can be effective in controlling COVID-19 and
emphasized the implementation of early and strong measures. These
studies, however, are based on limited data sets and did not specify
what combinations of prevention and control measures they mean with
“weak” and “strong.” Thus, it is not possible to draw conclusions
about the effectiveness of specific quarantine strategies.
The indirect evidence is limited to four cohort studies and 15 modeling
studies that used data from SARS and MERS outbreaks. For the
effectiveness of quarantine for individuals who were in close contact
with a SARS or MERS case, studies consistently confirmed the
effectiveness of quarantine but focus mostly on quarantine for
individuals who were in contact with confirmed cases. A modeling study
from Taiwan showed that even with a very low quarantine rate (4·7% of
those who should have been quarantined), a substantial number of SARS
cases and deaths could be prevented.36 The evidence on
the comparative effectiveness of different types of quarantine was
inconclusive.
Only three studies addressed the effectiveness of quarantine for people
who traveled from a region with a high rate of SARS
transmission.28,36,43 The number of infections and
deaths averted with quarantine was substantially lower than for the
quarantine of people exposed to SARS cases.
Limitations in the body of
evidence
The applicability of the results
from SARS and MERS studies is likely to be limited because most models
assumed that infectiousness starts with symptom onset. Preliminary
estimates of the basic reproduction number of SARS-CoV-2 range from 2·8
to 5·5.4,48,49 Models have shown that the
effectiveness of quarantining individuals during outbreaks of diseases
with presymptomatic infectiousness and a basic reproduction number of
>2·5 is limited. Based on estimates of a basic reproduction
number of 3·8 (95% CI, 3·6 and 4·0), Read et al. state, in an
unpublished article, that 72% to 75% of the transmission must be
stopped by control measures for COVID-19 infections to stop
increasing.4
Our report is not applicable to community quarantine, which was outside
the scope of this review.
Limitations of the review
Because of time constraints, we conducted a rapid review and abbreviated
certain methodological steps of the review process. Specifically, we
dually screened only 30% of the titles and abstracts; for the rest,
single screening was applied. A recent study showed that single abstract
screening misses up to 13% of relevant studies.50 In
addition, we applied a single risk of bias assessment, data extraction,
and certainty of evidence rating, with a second person checking the
plausibility and correctness. These steps are prone to human error and
with limited quality assurance with a second, independent person
conducting all steps, we introduced some risk of error to this rapid
review. Nevertheless, we are confident that none of these methodological
limitations would change the overall conclusions of this review.
5 Conclusion
Despite the limited evidence on quarantine to control COVID-19, studies
consistently concluded that quarantine is an essential public health
measure to control the spread of severe coronaviruses. For both
effectiveness and resource use, early implementation of quarantine seems
to be key. In addition, studies showed that effectiveness of quarantine
of individuals depend on the infectious disease biologic dynamics as
well as transmissibility, both areas that are still not clarified for
COVID-19.