Photo taken on Sept. 24, 2020 shows the NHS COVID-19 app displayed on a phone on Whitehall in London, Britain. On Thursday, more than one million people have downloaded the British government's long-anticipated contact-tracing NHS COVID-19 app for England and Wales within its first day of launch. The official NHS COVID-19 app instructs users to quarantine for 14 days if it detects they were nearby someone who has the virus. (Photo by Tim Ireland/Xinhua)

Photo taken on Sept. 24, 2020 shows the NHS COVID-19 app displayed on a phone in front of a tourism merchandise store on Westminster Bridge in London, Britain. On Thursday, more than one million people have downloaded the British government's long-anticipated contact-tracing NHS COVID-19 app for England and Wales within its first day of launch. The official NHS COVID-19 app instructs users to quarantine for 14 days if it detects they were nearby someone who has the virus. (Photo by Tim Ireland/Xinhua)

Photo taken on Sept. 24, 2020 shows the NHS COVID-19 app displayed on a phone in Parliament Square in London, Britain. On Thursday, more than one million people have downloaded the British government's long-anticipated contact-tracing NHS COVID-19 app for England and Wales within its first day of launch. The official NHS COVID-19 app instructs users to quarantine for 14 days if it detects they were nearby someone who has the virus. (Photo by Tim Ireland/Xinhua)

Photo taken on Sept. 24, 2020 shows the NHS COVID-19 app displayed on a phone outside Westminster tube station in London, Britain. On Thursday, more than one million people have downloaded the British government's long-anticipated contact-tracing NHS COVID-19 app for England and Wales within its first day of launch. The official NHS COVID-19 app instructs users to quarantine for 14 days if it detects they were nearby someone who has the virus. (Photo by Tim Ireland/Xinhua)

Photo taken on Sept. 24, 2020 shows the NHS COVID-19 app displayed on a phone in front of a red telephone box in London, Britain. On Thursday, more than one million people have downloaded the British government's long-anticipated contact-tracing NHS COVID-19 app for England and Wales within its first day of launch. The official NHS COVID-19 app instructs users to quarantine for 14 days if it detects they were nearby someone who has the virus. (Photo by Tim Ireland/Xinhua)

Photo taken on Sept. 24, 2020 shows a QR code to be scanned with the NHS COVID-19 app before entering the venue in Westminster, London, Britain. On Thursday, more than one million people have downloaded the British government's long-anticipated contact-tracing NHS COVID-19 app for England and Wales within its first day of launch. The official NHS COVID-19 app instructs users to quarantine for 14 days if it detects they were nearby someone who has the virus. (Photo by Tim Ireland/Xinhua)