Table 3.

A comparison of study design and structure of the research.

Study	Study design	Participants, n	Age	Follow-up duration (study period)
Bourdon et al [23]	Online surveys on patient and medical staff satisfaction with the mobile app and the wearables	12 patients and 24 medical staff	Patient mean age: 25 years; no information for medical staff	No follow-up
Huckins et al [24]	Observational cohort study measuring behaviors through the StudentLife smartphone sensing app	500	Mean: 40.7 (SD 20.3; 0.6-92) years. The number of patients older than 60 years was small.	No follow-up
Bae et al [25]	Observational data collection that helped develop predictive models. Participants that were already enrolled in ongoing epidemiologic studies were approached to use this app.	>2 million users; 75% female	Mean: 41 (range: 18-90) years	The launching of the COVID Symptom Study app occurred in the United Kingdom on March 24, 2020, and in the United States on March 29, 2020. 265,851 individuals were enrolled by March 27, 2020.
Drew et al [26]	Observational study on the COVID Symptom Tracker mobile app	5 hospitalized patients and 5 doctors	Patients range: 45-61 years	No follow-up
Ben Hassen et al [27]	The StudentLife app was used for smartphone mobile sensing. Ecological momentary assessments were used to assess depression and anxiety.	217; 67.8% (n=147) were female	Range: 18-22 years at the time of enrollment	178 (82.0%) students provided data during the Winter 2020 term (January 6 to March 13, 2020).
Kodali et al [28]	Observational study using descriptive statistics and thematic analysis on the mHealtha app Arogya Setu.	503 most relevant reviews were identified based on the Google algorithm	Not reported	All reviews that were available publicly and posted in English by the users until April 21, 2020, were included. The start date of app reviews collection was not reported.
Medina et al [29]	Observational cohort study carried out at the Cleveland Clinic, OH, US. It included a self-monitoring app for patient engagement and early intervention.	COVID-19 patients enrolled by May 25, 2020: 1924. Most (85%) patients were enrolled 5 days from symptom onset.	25% (n=483) were older than 60 years, and 3.5% (n=67) were younger than 18 years.	Engagement with MyCare Companion app reached 32%; 25% continued under monitoring for longer than 14 days due to persistent symptoms.
Menni et al [30]	Observational data collection and statistical analysis that helped develop predictive models	Symptoms were reported by 2,450,569 from the UK and 168,293 from the US	Average age for tested positive, tested negative, and not tested: (UK: 41.25, 41.87, and 43.38; US: 41.87, 47.25, and 53.00).	Data analyzed had been collected between March 24 and April 21, 2020.
Ros and Neuwirth [31]	A tutorial feedback survey was conducted. User feedback was requested from health care workers and responders about the presented global public health educational outreach technology.	12,516 users, learners, health care workers, and responders downloaded the app in 1 month.	Not provided	366 replies received during the first 72 h of deploying the survey. During this time period, there were 512 subscribers that had downloaded the app (71.48% response rate).
Timmers et al [32]	Observational cohort study (based on the data collected at the ETZb hospital), assessed the use of the app as well as its usability. Data were gathered for health care providers and policy makers.	6194 individuals downloaded the app.	Average: 50.87 years	The study focused on data collected between April 1-20, 2020. The app was being used by over 15 hospitals in the Netherlands, Belgium, and Germany, accumulating over 30,000 downloads.
Yamamoto et al [33]	Proof of concept and practical use study in a real-world setting. The study aimed to develop a PHRc-based COVID-19 symptom-tracking app to determine whether PHRs could be used for efficient health observation outside a traditional hospital setting. The practical aspects of health observations for COVID-19 using the smartphone or tablet app integrated with PHRs was demonstrated. Moreover, a usability evaluation of the app was carried out based on interviews with help desk managers of the app.	In the context of the active epidemiological investigation period (from March 6-19, 2020) at Wakayama City Public Health Center, 72 individuals who had close contact with a COVID-19 confirmed case were discovered. Among them, 57 had adopted the use of the health observation app.	N/Ad	The active epidemiological investigation period was carried out from March 6-19, 2020, at Wakayama City Public Health Center. In this period 57 of 72 individuals (health observers) adopted the use of the app. By mid-May, the app had been used by more than 20,280 users and 400 facilities and organizations. These included companies, schools, hospitals, and local governments across Japan.
Zamberg et al [34]	Utilization-focused evaluation study to identify the use of an mHealth platform for information sharing	125 members of the hospital staff	25-30 years: 28 members; 31-35 years: 24 members; 36-40 years: 18 members; 41-50 years: 29 members; 51-60 years: 24 members; >60 years: 2 members	The mHealth platform was used for 18 days from February 25, 2020, until March 13, 2020.

^amHealth: mobile health.

^bETZ: Elisabeth Twee Steden.

^cPHR: personal health record.

^dN/A: not applicable.