  The COVID-19 pandemic has prompted countries around the world to introduce
smartphone apps to support disease control efforts. Their purposes range from
digital contact tracing to quarantine enforcement to vaccination passports, and
their effectiveness often depends on widespread adoption. While previous work
has identified factors that promote or hinder adoption, it has typically
examined data collected at a single point in time or focused exclusively on
digital contact tracing apps. In this work, we conduct the first representative
study that examines changes in people's attitudes towards COVID-19-related
smartphone apps for five different purposes over the first 1.5 years of the
pandemic. In three survey rounds conducted between Summer 2020 and Summer 2021
in the United States and Germany, with approximately 1,000 participants per
round and country, we investigate people's willingness to use such apps, their
perceived utility, and people's attitudes towards them in different stages of
the pandemic. Our results indicate that privacy is a consistent concern for
participants, even in a public health crisis, and the collection of
identity-related data significantly decreases acceptance of COVID-19 apps.
Trust in authorities is essential to increase confidence in government-backed
apps and foster citizens' willingness to contribute to crisis management. There
is a need for continuous communication with app users to emphasize the benefits
of health crisis apps both for individuals and society, thus counteracting
decreasing willingness to use them and perceived usefulness as the pandemic
evolves.
