Rapid antigen testing helps decrease the prevalence of SARS-CoV-2 in Slovakia

In Slovakia, in counties subject to two rounds of rapid antigen testing for SARS-CoV-2 where those who tested positive then isolated, the approach helped decrease the prevalence of positive tests by more than 50% in a week - all while primary schools and workplaces remained open.

"While it was impossible to disentangle the precise contribution of control measures and mass testing," the authors said, mass testing is likely to have had a substantial effect, their modeling showed.

Applying mass testing may provide a valuable tool in future containment of SARS-CoV-2 elsewhere, they say. Compared to mandating closure of schools and non-essential businesses, which has had an unprecedented economic effect worldwide during the COVID pandemic, mass testing campaigns for SARS-CoV-2 - which can be conducted while such places remain open - are an alternative way to identify and target infectious individuals without much added burden to those who are not infectious.

In October and November 2020, to identify cases at scale and rapidly reduce transmission, in order to ease the conditions of lockdown, Slovakia used rapid antigen tests in a campaign targeting the whole population.

More than five million rapid antigen tests were conducted in a pilot, a first round of national testing, and in a second round targeted to high prevalence counties. More than 50,000 participants tested positive. Combining the pilot results with the ones from the two rounds of testing, each round of mass testing was estimated to have reduced observed infection prevalence by 56%, say Martin Pavelka et al.

The 41 counties with two rounds of testing likely reduced infection prevalence by 81% within two weeks. Further modelling by Pavelka et al. suggests the observed reductions could not be explained solely by infection control measures but required the additional impact of isolation of those who tested positive.

"The observational nature of this study made it difficult to separate the effects of the mass testing campaigns from the other non-pharmaceutical interventions introduced over the same period," say the authors. "Nevertheless, a greater than 50% decline in infection prevalence within one week is striking, particularly while primary schools and workplaces were mostly open." For comparison, a month-long lockdown in November in the United Kingdom led to just a 30% decrease in prevalence.