  The novel Coronavirus disease (COVID-19) is a severe respiratory infection
that officially occurred in Wuhan, China, in December 2019. In late February,
the disease began to spread quickly across the world, causing serious health,
social, and economic emergencies. This paper aims to forecast the short to
medium-term incidence of COVID-19 epidemic through the medium of an
autoregressive integrated moving average (ARIMA) model, applied to Italy,
Russia, and the USA The analysis is carried out on the number of new daily
confirmed COVID-19 cases, collected by Worldometer website. The best ARIMA
models are Italy (4,2,4), Russia (1,2,1), and the USA (6,2,3). The results show
that: i) ARIMA models are reliable enough when new daily cases begin to
stabilize; ii) Italy, the USA, and Russia reached the peak of COVID-19
infections in mid-April, mid-May, and late May, respectively; and iii) Russia
and the USA will require much more time than Italy to drop COVID-19 cases near
zero. This may suggest the importance of the application of quick and effective
lockdown measures, which have been relatively stricter in Italy. Therefore,
even if the results should be interpreted with caution, ARIMA models seem to be
a good tool that can help the health authorities to monitor the diffusion of
the outbreak.
