When coronavirus cases fell to devastating levels in much of Europe and the United States late last year, one country was able to get its outbreak under control with extensive testing. In October and November, after a brief lockdown, Slovakia tested a large percentage of its population in several rounds of rapid mass antigen tests. Unlike gold standard polymerase chain reaction (PCR) tests, this approach does not require special laboratory analysis and, unlike days, can often return results in about 15 to 30 minutes. (The U.S. Food and Drug Administration recently approved several rapid COVID tests for over-the-counter use.)
Within a week, the prevalence of COVID decreased by 58 percent in countries in Slovakia where two mass tests were performed. Researchers reported in late March science. Additional modeling indicated that case numbers were down by an estimated 70 percent compared to a scenario of uncontrolled growth at the rate observed before the mass testing began. The impact of public health measures like bans and social distancing wasn’t enough to explain the decline in cases – mass testing must have had a significant impact. While the approach may not work everywhere, the results support population-wide rapid testing, when combined with other measures, as an important tool in combating the pandemic.
Scientific American spoke to Martin Pavelka, an epidemiologist with the Slovak Ministry of Health, about the country’s mass testing efforts and whether this strategy could be applied in the US and elsewhere.
[An edited transcript of the interview follows.]
How did this mass testing program start?
It was basically just an idea. But because we are a small country, it is much easier to implement ideas. There are institutions discussing this – there are about five epidemiologists across Slovakia [in charge of these decisions]. We sit down every Thursday and basically make up our minds. All of this happened within two weeks. We asked the army to organize that.
I don’t think the US could repeat this approach [on a broad scale]. I mean over 300 million people – it’s just too much. But for smaller countries – I could see this work in Estonia, I could see it work in Portugal, I could see this work in Ireland.
Why wouldn’t the strategy work for larger nations? Do you need medical expertise to perform the tests? I mean, couldn’t you have some kind of test at home?
It was a massive campaign. I think this is a limitation in larger countries that have tried to replicate it. Austria tried and couldn’t make it. In Slovakia, 40,000 military personnel supported the entire intervention. We had 20,000 medical staff because it was a nasopharyngeal [deep nasal] Swab so you need to be trained to manage it.
Some home tests are already available in the US, but they are not very common. You’re just beginning to come out. The market is changing. I think Siemens is now offering a home test kit in Europe [Germany and Austria].
How well did the mass tests work in Slovakia?
The politicians thought it would solve everything. And I think it had a massive impact. But two to three weeks after that [initial rounds of mass testing]We had an increase in cases again, which is expected as the intervention cannot last forever. It’s like a lockdown: once you open the country, the falls will go up. The massive increase was just before Christmas. In January we repeated the whole exercise and we had [another] Round of mass testing. We are writing a second study on this. We are still in the process of analyzing the data.
At this moment we have continuous in Slovakia [weekly] testing. All residents who do not isolate and do not work from home are asked to take a test at least once a week. You will receive a certificate and a negative certificate is required to enter jobs. To go to the bank, tax office or post office, you have to show your negatives. And it can’t be older than seven days.
Our reproduction number [the average number of cases one infected person produces in a population] Right now it’s around 0.8 so our cases are coming down. And this in a situation in which almost 100 percent of all samples analyzed are the B.1.1.7 mutation [a variant of the coronavirus that was first identified in the U.K.]which has a much higher reproduction number.
What effect does a vaccination have, if any? What about other interventions?
In terms of vaccination, Europe is lagging behind. [As of early April]Only 10 percent of Slovak residents received at least one shot. Although there will of course be some effect, this alone cannot explain such a low reproduction number. There has to be an element [from] the mass test. We basically also discussed that in the study. The 58 percent decrease in COVID prevalence is a combined effect of it all. It is not possible to calculate “a third of that is the bulk test” or a quarter or a half. It’s just not possible. The next thing we can get is the math model we created. We showed that even if the lockout was perfect, such a rapid decrease in prevalence could not be explained. So we could say: “There has to be some effect of the mass tests.”
Just for comparison, the UK had a lockdown all November. It was just as strict as here in Slovakia…. All leisure activities were restricted; People were asked to stay home. It took the UK a month to [reduce cases] by 30 percent. We had a 58 percent drop in Slovakia in one week.
If a person in Slovakia or their family member tests positive, is the isolation or quarantine voluntary, or is there enforcement?
Everything here is voluntary. The amount of policing we need … just isn’t possible. But the Slovaks are very afraid of the virus – much more than in the Czech Republic, for example. In the first wave [here]I was very surprised that everyone started wearing face masks overnight. Nobody questioned that.
People are asked to self-isolate along with all of their household members for 14 days. This is the second most important finding of our mathematical model: We tried to find out what, in particular, makes the mass tests successful. We had two scenarios in our model. We had a scenario where all household members would be quarantined if they had a positive case. In this scenario, one round of mass tests was enough to reduce the prevalence [the observed] 58 percent. Then we had a scenario where only the infected person was quarantined but the household members were not. We couldn’t find a measured effect in this scenario. While our model says that one round of testing is sufficient to observe such a rapid suppression of prevalence, we know that there must have been an in-game lockdown, as not all households were isolated [to the extent] our model demanded.
There has been some debate about the accuracy of rapid tests. How accurate are they?
It really depends on the test. I think everyone gets confused. An antigen test is not the same as any other antigen test. From our own experience, SD Biosensors Standard Q. [antigen test] is very good. It’s easy to pick people out when they’re infected. There’s a Geneva [University Hospitals] Validation study with a view to CT [cycle threshold] counts and counts for the CT [of 18–22]there is 100 percent agreement with the PCR test. [Editor’s Note: CT is a measure of how much amplification is required to detect a virus using PCR tests. While CT is not standardized across tests, the lower the CT, the more virus is present, and the more infectious the individual is thought to be].
In our study, the specificity was [a measure of how well a test detects true-negative cases] was almost 100 percent. Of course we will have some false positives. Many scientists were afraid [we would have] Thousands upon thousands of false positives; We’re talking hundreds. We have identified more than 50,000 infected people, so it’s worth getting a few hundred false positives.
Under what conditions do you think a rapid antigen test would be most useful?
It’s especially useful when things get out of hand. If you suddenly have an outbreak or have a large, widespread event and you are experiencing a very high growth rate, this is a perfect intervention. They put people in a week-long ban and then test them. You could test a state; You could test a city. And that brings things back to normal – you could lose weight [cases] by 50 percent. And then you can bring back the usual testing and tracing, you can bring back the traditional methods when the epidemic is at a more stable, more manageable level.
The second thing is: it actually gives you a little more freedom. I mean, you can’t keep people in jail forever. You will experience COVID fatigue. People will find ways to get around the rules. From own experience, [in Slovakia]We have officially closed gyms, but I know at least three gyms in my district that are open. Even so, our cases are falling. [So the testing] brings people at least a certain amount of freedom.
How will the rapid tests fit when more and more people are vaccinated?
Vaccines are the ultimate solution. Bulky antigen testing in Slovakia will eventually fade. I can’t tell you when Is it when a third of the population is vaccinated? Maybe half the population? I dont know. It will be very difficult to adhere to the restrictions or even test people if you don’t have transmission because people are vaccinated. But even after people have been vaccinated that we could find some use for antigen testing, there are groups of people who are not vaccinated. And you could just mass test everyone in the cluster.
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