COVID-19—a very visible pandemic

Johan Giesecke¹ referred to the COVID-19 pandemic as an invisible pandemic, estimating that 25% of the Stockholm population was infected by the end of April, 2020, of which 98–99% are unaware of being infected. On April 1, 2020, the media reported that half of the Swedish population might be infected by the end of April, 2020.² More conservative estimates suggested that at least one-third of the Stockholm population may be seropositive by mid-May, and later that Stockholm might reach herd immunity by mid-June.3, 4 With a belief that Sweden is now close to herd immunity, many respiratory symptoms are falsely assumed to be caused by COVID-19, and because of the limited availability of testing unless a patient requires hospital care, many believe they are, or have been, infected.

Findings from studies in other European countries have revealed a low seroprevalence, and WHO has recommended countries not to rely on herd immunity. Although the numbers are not entirely similar, plotting results presented in the media against the reported cases per million inhabitants (with a lag of 2–4 weeks, since exact sampling dates are unknown; appendix) gives an estimate of a 3·8% seroprevalence in Sweden, which is in line with media reports.⁵ The media reports on how close Sweden is to herd immunity might cause public underestimation of the severity of the outbreak, and a false belief that many are already immune. Thus, there is an urgent need for large-scale and continuous serological screenings, and it is time to realise that there might a long way to go until herd immunity is established in Sweden.