Is seasonality a major factor in rise of Covid-19 cases in Europe?

GlobalData Healthcare 5 November 2020 (Last Updated November 5th, 2020 13:06)

Is seasonality a major factor in rise of Covid-19 cases in Europe?

Most of the countries in Europe are going through the second wave of Covid-19 and seeing an increase in hospitalisations, the number of patients needing oxygen therapy, and mortality. The recent increase observed in daily confirmed cases coincided with the start of the autumn and winter weather. This seasonality effect needs to be explored further to understand the role of cold weather in the surge of Covid-19 cases.

Figure 1 shows the number of daily new cases in five European countries (5EU: France, Germany, Italy, Spain and the UK) since March 2020. After the initial peak of daily new cases in April, cases started to decline in the 5EU. However, cases have started to rise simultaneously in these countries, to levels more than twice the initial wave, during the start of the colder weather. This had led to some researchers implying that Covid-19 is seasonal like influenza, and the peak of the cases will occur in the autumn and winter. Academic papers, as well as news articles have been published suggesting a strong seasonal role in the surge of cases.

The alternative argument is that the countries in Europe reopened their economies when the infections were not fully under control. Opening the economy, including schools, universities, and workplaces has simply provided the fertile ground for the rapid rise of cases. The surge of Covid-19 cases in India and in southern states of the US in the summer suggests that seasonality did not play a crucial role in these countries. New Zealand and Australia also managed to control the surge of Covid-19 cases during the winter in the Southern hemisphere. The more plausible reason for a rise in cases in Europe currently is related to people interacting indoors with poor ventilation, which increased the risk of transmission.

Covid-19 is extremely contagious, and the number of cases and deaths could rapidly spiral out of control if a country fails in its effort to control the spread of the virus in the vulnerable population. Western Europe is currently struggling to provide hospital care for its population due to the surge in cases. France and the UK are in national lockdowns to reduce the demand to health services. As people congregate more in indoor spaces during the winter, it remains to be seen if these lockdowns will be as effective as in the summer.

GlobalData believes that there is not enough evidence to suggest that SARS-CoV-2 has become a seasonal virus. But there is growing evidence to suggest seasonal effect will probably contribute to bigger winter outbreaks if this virus becomes endemic in the future. This assumption is on the basis that respiratory viruses spread more readily in colder weather.

Figure 1: Covid-19 Daily New Cases In the 5EU, 1 March–28 October.

Credit: GlobalData, Pharma Intelligence Center; Ourworldindata.org.

5EU= France, Germany, Italy, Spain and the UK.