  The COVID-19 pandemic has caused unprecedented disruption, particularly in
retail. Where essential demand cannot be fulfilled online, or where more
stringent measures have been relaxed, customers must visit shop premises in
person. This naturally gives rise to some risk of susceptible individuals
(customers or staff) becoming infected. It is essential to minimise this risk
as far as possible while retaining economic viability of the shop. We therefore
explore and compare the spread of COVID-19 in different shopping situations
involving person-to-person interactions: (i) free-flowing, unstructured
shopping; (ii) structured shopping (e.g. a queue). We examine which of (i) or
(ii) may be preferable for minimising the spread of COVID-19 in a given shop,
subject to constraints such as the geometry of the shop; compliance of the
population to local guidelines; and additional safety measures which may be
available to the organisers of the shop. We derive a series of conclusions,
such as unidirectional free movement being preferable to bidirectional
shopping, and that the number of servers should be maximised as long as they
can be well protected from infection.
