Why it is difficult to control epidemic outbreaks in a world that moves so much

In the last 20 years our way of moving has changed radically, we are used to stepping on an airport several times a year, either for work or to go on holiday. According to IATA data, in less than 15 years the number of trips has doubled, with forecasts of more than 8.2 billion passengers worldwide by 2035. Such growth has made the world seem smaller every day. Not only for us but also for infectious diseases. And that's where the problems start.

In controlling a pandemic, the key is to detect the first cases as early as possible and confine them before they can generate other outbreaks. The time between infection and insurgency of the disease is what is defined in epidemiology as the incubation period. During this period, the infected person shows no symptoms and continues to live his or her normal life, ignoring the fact that he or she is spreading the infection. This period, however, can vary greatly between diseases. This implies that analyzing the data of an epidemic is like looking back in time: the new cases we see today are the result of infections that occurred days ago, depending on the disease.

In the case of COVID-19 the severity of symptoms can vary greatly from person to person, with a relatively high percentage of asymptomatic patients -people who have the virus in their blood without showing any symptoms- making it possible for the infected person not to notice the disease and not to take measures to prevent its spread.

IFISC (UIB-CSIC) researcher Sandro Meloni has published "Why it is difficult to control epidemic outbreaks in a world that moves so much", an outreach article analysing this problem in The Conversation, a portal for news and analysis written by the academic and research community and aimed directly at society.