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1. Introduction
Contact tracing aims at reconstructing and identifying the social interactions of an infected person. It does not necessarily require knowing the exact movements of infected people, nor does it need to use digital tools to collect information. In the past, the movements of infected individuals were indeed recorded on paper on the basis of oral reports and interviews.

Contact tracing, together with other containment measures, can contribute to lowering the basic reproduction number of an infection (denoted as R_0), which is the average number of cases directly generated by one infected person[1]. The value of R_0depends on different factors, including the infectiousness of the pathogen, the number of contacts of each infected person and the duration of the infection. Currently, without measures of containment in place, the R_0of the COVID-19 is around 2.5[2].

Until a vaccine is developed, and given that the virus is infectious during the incubation period, social distancing is necessary to bring this number down. Nonetheless, since household contacts are responsible for 39% of contagions, reducing contacts across the entire population by 90% is insufficient to bring the value of R_0below 1[3]. In sum, in areas where the disease has already reached epidemic proportions, lockdowns and stay-at-home orders can only slow down the contagion curve, but not reverse it.

In these types of scenarios, contact tracing is even less effective than social distancing and altogether insufficient as a stand-alone measure. However, it can contribute to closing the value of R_0to 1 if used in conjunction with other measures. Contact tracing can be even more effective when the outbreak has not yet become an epidemic, or when the epidemic is waning, by slowing down the spread of the virus, and by helping to target virological testing. It is thus a useful instrument in the fight against the COVID-19 epidemic.

In advanced economies, data collected from handheld devices such as smartphones and tablets can be used for contact tracing. In this respect, the crucial information is the users’ location (specifically in relation to confirmed cases) and identity. With regard to the former, it can be obtained from: a) multilateration of radio signals between cell towers and phones with a location accuracy of hundreds of meters; b) satellite-based positioning systems with a location accuracy down to a few meters; c) Bluetooth based systems aimed not at localizing devices, but at registering close interactions between users.

With respect to the identification of users, while necessary to the functioning of the system, transferring personal information to public authorities can endanger privacy and data confidentiality. Of course, these risks must be weighted against the benefits of contact tracing in reducing infections in the population.

In response to the COVID-19 epidemic, China has implemented a digital tracing system on a very large scale. Everyday, chinese contact tracing apps are utilized by hundreds of millions of people to enter public spaces and to travel across the country. However, they have also raised concerns in terms of privacy and data confidentiality.

In Europe, where contact tracing apps will be deployed over the coming weeks, these principles are regarded as individual rights. A comparison between the Chinese and European approaches is helpful to understand how to make contact tracing effective, as much as safe in terms of data protection. More in general, it can offer useful insights on how to safeguard individual rights, while pursuing effectiveness in public action.

2. Contact tracing in China
Contact tracing has been central to the Chinese anti-epidemic strategy, along with social distancing, virological testing and the widespread use of personal protective equipment. As early as January 21, the Joint Prevention and Control Mechanism of the State Council (国务院联防联控机制) emphasized the importance of “discovering, reporting, isolating and treating in advance ( 早发现、早报告、早诊断、早隔离、早治疗)”, and stressed the need to carry out and standardize close contacts tracing[4].

Over the following days, the government initiated a data collection and analysis effort aimed at monitoring and predicting population flows, as well as at providing the tools for early warning of close contacts[5]. Based on the data gathered and shared by a wide range of public bodies (including the central government, territorial administrations, public telecommunications companies and regulators), as well as by the WeChat and Alipay[6], China developed a range of contact tracing tools to identify and isolate COVID-19 patients[7]. At the national level, all these tools rely on the country’s digital ID and real-name registration systems, both well-established in China.

The digital ID system, run by the country’s Ministry of Public Security, is based on the ‘Resident Identity Card’ card, the jumin shenfenzheng (居民身份证). The card contains a wide spectrum of personal information, including biometric and health data, criminal record, as well as travel details such as plane, train and long-distance bus reservations[8]. The Resident ID card is also required to register a new mobile phone number. The Chinese authorities can thus easily access citizens’ health status during ID checks, keep up with their travels on the national transportation network, and track their phone.

The other essential ingredient in China’s contact tracing system is real-name registration, via the Resident ID Card and mobile phone number[9], to access the country’s main social media platforms (WeChat and Alipay). This is critical because, aside from developing the health code apps, WeChat and Alipay (and, to a lesser extent, China’s main search engine Baidu) also provide essential contact tracing data such as GPS positioning[10], as well as users’ personal connections and web search data.

In sum, thanks to the digital identity system and to real-name registration on web platforms, Chinese contact tracing apps can tap on an immense reservoir of information. However, integrating data at a national level has proven to be a challenge[11] . As a result, China’s contact tracing tools are not unified, but they instead fall into two categories, depending on their scope and on the administrative level of implementation.

^Note

1.  https://www.iss.it/primo-piano/-/asset_publisher/o4oGR9qmvUz9/content/id/5268851 ↑

2.  Kretzschmar, Mirjam and Rozhnova, Ganna and van Boven, Michiel, Isolation and Contact Tracing Can Tip the Scale To Containment of COVID-19 In Populations with Social Distancing (3/23/2020). Available at SSRN: https://ssrn.com/abstract=3562458 or http://dx.doi.org/10.2139/ssrn.3562458 ↑

3.  Ibid ↑

4.  http://www.gov.cn/xinwen/2020-01/22/content_5471437.htm ↑

5.  https://mp.weixin.qq.com/s?__biz=MzU1Mzc4NTE1Nw==&mid=2247485418&idx=1&sn=838e74bbaf994049f1067a3bb9026567&chksm=fbecc5c0cc9b4cd618379bb0400a65ea75c378b00153e30ecc59a946ee39b6f92134bcfbeefd&scene=21#wechat_redirect ↑

6.  There are strong indications that GPS location data from WeChat and Alipay are fed into the contact tracing apps, but so far this has not been confirmed officially. https://www.colabug.com/2020/0409/7231279/ ↑

7.  The first of such tools, the “Close Contact Measurement Tool” (密切接触者测量仪) recorded over 130 million queries just for days after its introduction on February 10. https://tech.chinadaily.com.cn/a/202002/17/WS5e4a4ac7a3107bb6b57a03be.html ↑

8.  http://www.gov.cn/zhengce/2011-10/29/content_2602263.htm ↑

9.  http://www.cac.gov.cn/2017-09/07/c_1121624269.htm ↑

10.  https://www.colabug.com/2020/0409/7231279/ ↑

11.  At the national level data are channeled into the National Integrated Platform of Government Services (全国一体化政务服务平台), which was established in November 2019. The platform aggregates data from the National Health Commission, The Public Ministry of Public Security, the MIIT (which collects the data from the mobile carries), as well as from the national railways and the civil aviation authority. It is not clear to what extent information gathered by local authorities and private companies is also channeled into the platform. http://www.gov.cn/zhengce/content/2018-07/31/content_5310797.htm ↑

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