“Covid-19: In the footsteps of Ernest Shackleton” is a brief communication, just published online in Thorax. It describes a cruise ship which set sail after the COVID pandemic was declared, en route for the Antarctic. All passengers had temperature checks on embarkation, but a week into the trip some passengers developed fevers and the trip was cut short. On finally arriving in Uruguay, all the passengers and crew were tested for COVID-19 (using RT PCR) before they got off the ship. The paper describes how 59% were COVID positive. The authors go on to report that 81% of COVID positive individuals had no symptoms.

It is difficult to find a reliable estimate of the number of COVID positive patients who have no symptoms. In early March, WHO suggested the figure might be only 1% (see WHO media briefing) – very different from the 81% figure found on the cruise ship. As countries progress out of lockdown, a high proportion of infected but asymptomatic individuals may mean that a much higher percentage of the population than expected may have been infected with COVID. These individuals may have immunity to COVID. This demonstrates the urgent need for accurate seroprevalence studies to estimate the overall population infection rate across the globe.

Alan Smyth, joint Editor-in-Chief of Thorax