Why should we care now?

Contact tracing as a personalization framework

Published: April 8, 2021


  • PCT's early warning signals will become increasingly useful with more dormant characteristics of the virus

Limitations and Open Questions

As computer scientists, we think about how a proposed solution will fare in a worst-case scenario. As discussed earlier, the PCT framework with warning signals strives to caution individuals earlier than without the warning signals. The usefulness of early warning signals will be more noticeable for a virus that exhibits dormant characteristics, i.e., the host is infectious without definite signs of being infected.

The following changes to the viral profile will increase its dormant characteristics.

  • Weaker tests & delayed results: In the absence of conclusive diagnostic tests, we will be likely to detect an infectious person. SARS-CoV-2's most conclusive test is through Real-Time Polymerase Chain Reaction Test (RT-PCR). The test's false-negative rate varies depending on the individual's viral load, with a minimum of 33% at the peak viral load. The test results take at least a day to two to return. Thus, a worst-case virus will likely have a higher false-negative rate with a longer turnover time. As an aside, the mega-diagnostic platforms, proposed in Bill and Melinda Gates, 2021 Annual letter focused on better preparedness to future pandemic, serve the purpose of faster turnover.
  • Inconclusive symptoms & harsher health-impact: If an infected individual shares a symptom profile with other common diseases, it is likely to be ignored by an individual. Familiar stories have come up during the Covid-19 pandemic. SARS-CoV-2 virus exhibits such inconclusive signs of the virus combined with varying degrees of health-impact depending on individual characteristics. Thus, a worst-case virus will likely have more of such inconclusive signs for some people and have a harsher health impact on others.
  • Longer incubation period : If an infectious individual is unaware of the infection, they are likely to spread the infection. Recall that the incubation period is the time since infection before any symptoms appear. SARS-CoV-2 has a mean incubation period of five days, so a longer incubation period will likely to result in more infections per individual (i.e. higher reproductive number R).
  • More asymptomatic population & their infectiousness: An estimated 20-40% of the population does not show any symptoms throughout the time they are infected. However, their infectiousness (likelihood to infect others) is also roughly 30% of those who exhibit symptoms. Thus, a worst-case virus will likely have a larger proportion (less than 100%) of asymptomatic population with higher infectiousness.

Many future pandemic preparedness efforts are likely to be focused on rapid vaccine development and testing platforms. These efforts will help us fight this worst-case virus. However, due to the speed and the scale with which digital contact tracing can be deployed, efforts to improve the existing contact tracing frameworks (e.g., PCT, PanCast) may prove equally beneficial.

Limitations and Open Questions