News August 21, 2020

Contact Tracing Model Shows Potential Impact Against COVID-19, Yet Obstacles Abound

While there is no national, cohesive COVID-19 contact tracing plan, SHP's Joshua Salomon writes that it's important to continue to invest in contact tracing capacity now, because once we can get a handle on the virus, the combination of testing, contact tracing and supported isolation will be essential to the containment and outbreak response.
A contact tracing app
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There is plenty of evidence that one of the keys to stopping the spread of COVID-19 is contact tracing: identifying those people who may have come into contact with an infected person in order to prevent further transmission.

The United States is the leader in global deaths from the virus, yet there is no national effort to adopt a national contact tracing plan. So public health departments in most states have established their own plans, hiring contact tracers to fan out in their community and build maps of those who have come into contact with those who have tested positive for the virus. The data let public health officials know where transmissions are happening and when it’s safe to ease up on lockdowns and quarantines.

Most importantly, contact tracing can lead to earlier identification of people who may be infected so that they can be encouraged to quarantine and isolate before they can pass infection along to others.

Stanford Health Policy’s Joshua Salomon, a professor of medicine and senior fellow at the Freeman Spogli Institute for International Studies, and colleagues developed a mathematical model to examine the potential for contact tracing to reduce the spread of the coronavirus. They modeled contact tracing programs in the context of relaxed physical distancing under different assumptions for case detection, tracing coverage and the extent to which contact tracing can lead to effective quarantine and isolation.

“The benefits of contact tracing depend substantially on adherence to isolation and quarantine among individuals who are traced, which could be enhanced through policy measures such as voluntary out-of-home accommodations, income replacement, and social supports,” Salomon and his co-authors write in this JAMA Network research letter. The other authors are Alyssa Bilinski, a PhD candidate in health policy at Harvard University, and Farzad Mostashari, MD, the founder and CEO of Aledade, Inc.

The model evaluates the benefits of contact tracing programs by simulating chains of transmission and then considering how these chains can be broken by diagnosing people who are infected, tracing their contacts, and then helping those contacts to avoid further transmission through self-isolation (for those who are known to be positive) or self-quarantine (for those who may have been infected). In the study, the authors look at different factors that can make the benefits of contact tracing larger or smaller in order to help health officials design, implement and benchmark the performance of contact tracing programs.

They found that detection of cases in the community and successful outreach to contacts both need to exceed 50% in order for contact tracing to reduce transmission substantially. But they also found that the most effective programs — those with high levels of testing, tracing, isolation and quarantine efficacy — could reduce overall transmission by almost half. Such a benefit would allow for substantial loosening of physical distancing measures and public health restrictions while still enabling control of COVID-19 spread.

But there are many obstacles at present that limit the ability to realize the maximum benefits from contact tracing programs, Salomon said, including the lack of national coordination and funding — and the large volume of ongoing transmission.

“With the epidemic continuing to rage in many places, and ongoing strains on testing capacity, a lot of contact tracing programs are really stretched to their limits,” Salomon said.

On the other hand, he noted there are examples of contact tracing programs that are achieving promising results in some states, including New York and Massachusetts.

“It is also important to continue to invest in contact tracing capacity now, because once we’re able to get our arms around the epidemic a little bit better, the combination of testing, contact tracing and supported isolation will be essential to containment and outbreak response.”

Joshua Salomon

Professor of Medicine
Salomon focuses on the measurement and valuation of health outcomes.
Joshua Salomon of Stanford Health Policy

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