What we should learn from digital contact tracing
Don't fall for the anti-hype. Digital contact tracing works, but its integration into public health, and communication to the public, are massive challenges.
This is part 3 of a 4+1 series on digital contact tracing. You can read the previous parts here:
Part 0: Digital Contact Tracing - a mini series in 4(+1) parts
Part 1: Why contact tracing needs to go digital
Part 2: Privacy in digital contact tracing
Part 3: Did digital contact tracing work?
As vaccines against COVID-19 became widely available, and the threat of high mortality or severe disease started rescinding, most countries eventually stopped their testing, contact tracing, and quarantining (TTIQ) efforts, and discontinued their digital contact tracing apps. Today, digital contact tracing is still employed in certain parts of the world, but the large-scale deployment has come to an end. Beyond the empirical evidence for its efficacy, what learnings can we draw from the historically biggest roll-out of digital epidemiology technology?
Privacy
First, the tradeoff between privacy and epidemiological impact is much smaller than generally perceived. Digital epidemiology is often perceived as weak on privacy, but the decentralized tracing protocols demonstrated that the goals of digital epidemiology needn’t be at odds with privacy. Interestingly, in surveys, many people reported not using digital contact tracing apps because of privacy concerns. One can’t expect the general population to always be on top of the privacy-relevant details of contact tracing protocols. Trust in technology is ultimately trust in the provider of the technology. If people don’t trust the providers - from governments to tech companies - then even the best privacy-preserving solutions will be rejected.
Privacy must be built into the technology from the start (privacy by design). Solutions that did not follow this principle - such as centralized approaches - argued that people should put their trust in central authorities to not abuse the data. However, even with the best of intentions, centrally stored data can lead to catastrophic data leaks at scale. In addition, the availability of information-rich data in central places often turns out to be too attractive. For example, despite assurances to the contrary, centralized contact tracing data in Singapore (which opted for a centralized approach) was used by police for criminal investigations on multiple occasions. Similarly, German police used data from the private, centralized presence tracing app Luca for criminal investigations (note that the official government app, CoronaWarnApp, uses decentralized presence tracing). Such abuses of trust will unfortunately hamper the widespread adoption of contact tracing apps, even of those that have privacy built in by design.
Communication
This leads us directly to the second learning, which is on the importance of good and continued communication. The epidemiological impact of digital contact tracing scales directly with the uptake rate. As the NHS COVID-19 app study showed, each additional percentage point would lead to around one percentage point in cases averted. One does not need to use advanced mathematics to understand just how impactful digital contact tracing could be if the vast majority of people would use it. But for this to happen, there needs to be clear communication on the trustworthiness of the technology (provided it exists), and continued dialogue about how the technology and the broader TTIQ method work. What might be obvious to a public health professional may not be so clear to the general population.
Digital contact tracing faced particular challenges, as people who are experts in technology often pronounced themselves critically, and without competence, on the epidemiological aspects, and vice versa. As a typical example, take the following excerpt from Buzzfeed, on April 29, 2020, a hot phase of digital contact tracing technology:
“My problem with contact tracing apps is that they have absolutely no value,” Bruce Schneier, a privacy expert and fellow at the Berkman Klein Center for Internet & Society at Harvard University, told BuzzFeed News. “I’m not even talking about the privacy concerns, I mean the efficacy. Does anybody think this will do something useful? … This is just something governments want to do for the hell of it. To me, it’s just techies doing techie things because they don’t know what else to do.”
If experts in privacy technology dismiss new digital epidemiology approaches out of hand, before it is deployed and before the evidence has been gathered, we should perhaps not be surprised that the general population does not adopt the technology broadly. This is particularly concerning as there is some evidence the perceived lack of benefit has been a main inhibitor of broad uptake. While it’s possible that the complete novelty of digital contact tracing combined with the shock of an unparalleled health crisis may have contributed to the cacophony of reactions, one can only hope that in a future pandemic, people will look at the now available empirical evidence before pronouncing themselves in public.
Once people start using a digital contact tracing app, communication doesn’t end there. The app is itself a major communication vehicle that countries and states have used in different ways, and we need to better understand what worked and what didn’t. The development of digital contact tracing apps was so fast that such considerations were initially not on any priority list. While this is understandable in the beginning when launching an app in response to a new pandemic, communication should have received major attention over the following weeks and months after release. Let me highlight two examples from the Swiss app which are likely representative of problems encountered elsewhere. First, the Swiss app decided early on that the app should primarily be a “background app”, meaning that it would simply do its job silently, and only alert the user if there was something to be concerned about, i.e. an exposure worthy of a notification. In contrast, other apps, such as the German Corona Warn app, were constantly communicating different risk levels to the users, using a color code. As a consequence, many Swiss users over time started to wonder whether the app worked at all, since it wasn’t signaling anything to them.
Second, many apps started to build additional information streams and functionalities into their contact tracing apps. For example, some apps started to integrate vaccination certificates into the contact tracing app, or dashboards about local disease activity. The Swiss app decided against such additional functionality, as there was concern that such bundling would make it harder to dismantle parts of the system once they were not necessary anymore. Which approach is more useful depends critically on an app’s objectives, but we should be mindful that communication from the app plays a key role in its future use.
Presence tracing
The third learning is that based on our current understanding of the dominant transmission mode of SARS-CoV-2 and other respiratory pathogens, it is likely that presence tracing will play a much bigger role than proximity tracing in future pandemics of respiratory diseases. Presence tracing has yet to be validated with empirical evidence, but it’s clear that future digital contact tracing cannot focus exclusively on transmissions over short distances. Presence tracing solutions have often been deployed with privacy as a secondary thought, if at all, and thus a particular focus should be put on developing standards to ensure deployed solutions benefit from the same privacy guarantees as decentralized proximity tracing. The lack of such standards would almost certainly lead to abuses of centralized data (as seen during the COVID-19 pandemic), which would erode trust in all digital contact tracing applications.
Digital Public Health
Fourth, a more general learning is that many healthcare systems still rely on extremely outdated technology (e.g. fax), or even manual processes. These systems need to rapidly advance their digital capabilities. The TTIQ methodology operates in an environment with many different stakeholders, making technical coordination even more important. Those aspects of the TTIQ pipeline that were not automated often proved to be the least reliable, especially as systems started to experience extreme stress when case numbers were high, giving end users the impression that the digital contact tracing app didn’t work when it would have been most useful.
Assessement and Collaboration
Fifth, the rapid development of contact tracing technology led to a wide range of terminologies, and approaches of assessing the performance and efficacies of digital contact tracing systems. Common frameworks to evaluate the apps, their impact, and terminology are urgently needed. Finally, and sixth, there is an urgent need for international standards for risk calculations (i.e. the conditions under which an app should trigger a notification). This will make apps not only more comparable, but it will also make their integration across international borders much easier.
While contact tracing has seen very rapid development during the early phase of the pandemic, its development has come almost to a complete stop. This isn’t smart. When the next pandemic hits (when, not if), we should not spend valuable time developing new technology under extremely difficult circumstances that could have been developed in quieter times before. As is always the case with infectious diseases, the earlier an intervention can have an effect, the more outsized its impact will be.