Yet a balance had to be struck between protecting a country and not unduly hindering international trade and commerce, and we have not found any evidence that the quarantine rules were ever widely used. Medical advances such as inoculation meant that countries could prioritise making sure that travellers were vaccinated against certain infectious diseases instead.
In an echo of this more pragmatic approach, the WHO is not currently recommending travel bans with the novel coronavirus, arguing that they are counterproductive. According to a WHO spokesperson: “This is because of the social disruption they cause and the intensive use of resources required.”
But countries have responded in different ways. Many have temporarily suspended all direct flights to and from China while others are repatriating their citizens and placing them in temporary quarantine. Travel restrictions also extend to airport health screenings, denying entry to foreign visitors who have recently been to China or Hubei province and restricting border crossings.
We have seen airports making health interventions before in response to outbreaks of infectious disease, including during the Sars outbreak of 2002-03, H1N1 in 2009 and Ebola in 2013-16. Then, as now, countries including the UK used temperature scans of passengers to identify those with a fever and also administered health questionnaires. In some cases, we have seen additional post-flight contact tracing to identify people who were sitting in close proximity with an infected passenger.
But whatever airlines do, viruses and pathogens will always catch a lift on aircraft. For example, while it is relatively easy to suspend direct flights from infected regions, it is far harder to trace passengers who arrive from an infectious area but who have travelled on several flights and changed planes (and sometimes airlines) en-route at an intermediate hub.
It doesn’t mean these interventions have no benefit, but it is likely to be modest. The rapid global spread of recent outbreaks has shown that they are usually introduced after the event and that their efficacy has been limited.
Their value is arguably more that it’s necessary for governments to be seen to be doing something to reassure their populations. Ultimately, the transmission of infectious disease is a risk we accept in exchange for the benefits of mass air travel. We just have to hope that we are sufficiently able to control diseases such that we never end up paying too high a price.