NEW YORK — Slovakian researchers have completed a study looking at the impact of population-wide rapid antigen testing on the prevalence of SARS-CoV-2 in that country and found that mass testing with such assays can significantly reduce the prevalence of the virus.
Their work is detailed in a paper published on Tuesday in Science.
Rapid antigen tests have been identified as a potentially key technology for slowing transmission of SARS-CoV-2. While they are not as sensitive as lab-based molecular tests, they are easier and cheaper to deploy and can, in theory, be conducted frequently enough to overcome any lack of sensitivity.
Modeling studies suggest that frequent and consistent testing can significantly reduce transmission of SARS-CoV-2 even when using lower performance tests, but there is limited data on the effectiveness of such approaches when applied in the real world.
Liverpool, England, has been running a COVID-19 testing pilot using a rapid antigen test from Pasadena, California-based Innova Medical Group to test around 40 percent of the city's population. The testing program identified several thousand COVID-19 positive individuals who might otherwise have gone undetected, though there was little evidence from Liverpool COVID-19 infection or hospitalization trends to indicate the testing program significantly reduced the spread of the virus.
The Slovakian study offers another look at the role rapid antigen testing might play in slowing the spread of SARS-CoV-2. Conducted in October and November 2020, the campaign ran 5,276,832 SD-Biosensor Standard Q rapid antigen assays testing more than 80 percent of the country's population between 10 and 65 years old along with older adults who were still a part of the workforce.
Based on their findings, the researchers estimated a decline in disease prevalence of 70 percent compared to a scenario where no steps were taken to mitigate spread. The researchers noted that the observational nature of the study "made it difficult to separate the effects of the mass testing campaigns from that of the other non-pharmaceutical interventions introduced over the same period," but said that their modeling indicated the decrease in prevalence could not be explained by these other interventions alone.
Testing was conducted in three rounds. The first round, a pilot, tested four of Slovakia's counties most affected by the virus. That was followed a week later with a round that tested the full population, which was followed a week later by a third round testing targeting high prevalence counties. The rounds tested, respectively, 87 percent, 83 percent, and 84 percent of the eligible populations and identified a total of 50,466 positive individuals.
The proportion of positive tests was 3.91 percent in the pilot round, 1.01 percent in the first round, and .62 percent in the second round.
In the four counties that participated in the pilot round, observed infection prevalence dropped by 56 percent between the pilot and first rounds and another 60 percent between round one and two, for a total decrease of 82 percent in two weeks.
In the 45 counties that were tested in round one and two, prevalence dropped by 58 percent between the two rounds of testing.
The reduction in prevalence varied widely among these 45 counties, however, from a low of 29 percent to a high of 79 percent.
Martin Pavelka, an epidemiologist with the Slovak Ministry of Health and first author on the study, said in an email that the researchers suspected economic factors were likely driving this variation.
"For this intervention to be effective, a positive case must isolate together with their household for two weeks," he said. "This may be difficult for some households in poorer counties and indeed some of the poorest counties in Slovakia are not responding to this intervention at all."
He said he and his colleagues are currently involved in a follow-up study exploring the causes in the variation in prevalence reduction.
The authors also noted that "data on hospital bed occupancy shows a sudden flattening from mid-November indicating a sharp decrease in new admissions consistent with a sizable reduction in new infections when mass testing campaigns occurred."
Pavelka said that Slovakia has continued to test roughly one-third of the country each week using rapid antigen tests and plans soon to release a follow-up study showing the results of that testing.