Active Symptom Monitoring Won’t be Effective in Controlling Spread of COVID-19 Once World Returns to “New Normal,” Study Suggests

Updated on May 27, 2020
An infected patient in quarantine lying in bed in hospital, coronavirus concept.

Individual quarantine – with rapid contact tracing and strict isolation measures – shown to be best defense against future outbreaks of the virus, says Virginia researcher 

As the number of new COVID-19 cases decreases and the world slowly resumes public activity in a controlled manner, a research study shows individual quarantines will be our best defense against future outbreaks of the virus.

“There will be a point in this pandemic where we will want to switch our resource allocation from social distancing towards early identification of cases, rapid and thorough contact tracing, and near-perfect isolation measures to effectively stop the chain of transmission and mitigate a resurgence of this disease,” said Lauren Childs, assistant professor of mathematics at Virginia Tech, who specializes in understanding the spread of infectious diseases. 

Her remarks come on the heels of research, published in the May edition of SIAM Newswhich indicates that of the two most common non-pharmaceutical interventions employed by governments and public health officials – individual quarantines and active symptom monitoring –  individual quarantine is more effective at curbing COVID-19 spread.

Applied as an intervention, active symptom monitoring means people identified as coming into contact with the virus are allowed to go about daily activity and are checked at regular intervals for signs of symptoms. They are only isolated after they become symptomatic. Individual quarantine, on the other hand, requires all people known to have been in contact with an infected person to be strictly quarantined for a period of 14 days.

Researchers examined each strategy in the context of the novel virus and found that although individual quarantine does impact a high number of people who may never catch the virus, it remains a far better strategy than active symptom monitoring due to the nature of the virus itself.

“What was done to control the Ebola virus outbreak in 2014-2016 won’t work for COVID-19,” said Childs, referring to how active symptom monitoring was used to control Ebola spread as healthcare workers returned to the U.S. from the front lines of the outbreak in Africa.

“Active symptom monitoring was highly effective at that time because symptoms were directly correlated to time of infectiousness,” she explained. “For COVID-19, monitoring of symptoms is insufficient to eliminate possible transmission because we have individuals who are infected but not showing symptoms.”

Approach 95 percent effective in stopping transmission 

Childs and coauthors from the Harvard T.H. Chan School of Public Health (see reference #7 in SIAM News article) found that when a new case of COVID-19 is identified, if nine out of 10 of that person’s contacts are identified within half a day, and if nine out of 10 of them are then placed into near perfect isolation – meaning zero contact with others – then transmission can effectively be stopped 95 percent of the time. In comparison, active symptom monitoring reduces transmission only 12 percent of the time.

“Right now, social distancing is our best option to reduce spread because community transmission remains widespread and we don’t have a good way to monitor who’s infected,” Childs said. “The more we are able to reduce community transmission to very small pockets, the closer we will be to transitioning to more targeted interventions.”

Childs is calling on regulators and health officials to consider the research – which is publicly available – to assist in developing frameworks for preventing transmission as the pandemic winds down and normal activities resume. One suggestion is to allocate more resources towards identifying and tracking infected individuals and ensuring individual quarantines are near-perfect, which would mean fully isolating people in their homes, or if that isn’t possible, in hotel rooms

“We’re not there yet, but once we’re in a position where we can more readily keep track of infectious individuals and who they contact, with the appropriate resources to track them and isolate them, individual quarantine will be the best strategy to avoid a resurgence of this pandemic,” Childs said. 

Society for Industrial and Applied Mathematics (SIAM), headquartered in Philadelphia, Pennsylvania, is an international society of more than 14,000 individual, academic and corporate members from 85 countries. SIAM helps build cooperation between mathematics and the worlds of science and technology to solve real-world problems through publications, conferences, and communities like chapters, sections and activity groups. Learn more at

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