A preprint, an unpublished non-peer reviewed study, posted on medRxiv looks at the effectiveness of population-wide rapid antigen test based screening in reducing SARS-CoV-2 infection prevalence in Slovakia.
This Roundup accompanied an SMC Briefing.
Prof Sheila Bird, Formerly Programme Leader, MRC Biostatistics Unit, University of Cambridge, said:
“Slovakia deployed 60,000 trained personnel and required minimal data when delivering the mass rapid testing programme described here. Slovakia achieved an uptake of over 80% of its 4 million eligible population. They used a nasopharyngeal-swab for rapid-testing by the SD Biosensor Standard Q antigen test, which is different to the INNOVA rapid-test which is offered in Liverpool and for use by tier 3 locations in the UK.
“Based on published validation studies, Slovakia assumed – but, unlike Liverpool, did not check – that, in its mass screening context, sensitivity of the test would exceed 70% (ie would identify 70% of those truly positive). Liverpool checked and, in around 5000 asymptomatic citizens, found the sensitivity of its INNOVA rapid-test to be below 50%.
“Slovakia deployed around 20 thousand medical staff and 40 thousand non-medical personnel to administer up to 4 million tests in 2 days (actually: 3.316 million tests in round 1): a rate of around 30 citizens tested per tester per day. Shifts were probably 10 hours long. This is very efficient and there was a high uptake of tests by the public.
“There are some potential confounding factors. A national lockdown was in force before Slovakia’s mass screening (round 1) on 31st October and 1 November. Additionally, previously Slovakia had no Test & Trace set-up akin to England’s. Hence, citizens who tested positive after rapid testing were asked to enter a 10-day long quarantine together with all members of the same household plus their self-traced contacts in the preceding two days in an attempt to reduce secondary transmission.
“Slovakia did not appear to restrict rapid-testing to those who were asymptomatic. Test-results were given on-site within 15-30 minutes and a medical certificate was issued to every participant confirming their infection status. Testing was not obligatory but residents who did not attend for mass screening were instructed to stay at home for 10 days or until the next round of screening. A test-negative certificate was required by employers to enter workplaces. In addition, various venues and public institutions inspected citizens’ certificates.
“There was minimal data-gathering as participant information was not collected, only each county’s number of rapid-tests and test-positives.
“Modelling was used to provide possible scenarios around the impact of mass testing based on different assumptions about the impact on the reproduction number of lock-down alone and in conjunction with mass testing. One would need to read the modelling more closely than I have done to check on the assumptions made about rapid-test sensitivity (which was not checked in this context) and about the lead-time that pre-symptomatic rapid-testing gives on RT-PCR testing (only after symptoms have developed). This lead-time is critical for the efficiency of quarantine (entire household of positive case; and their contacts 2 days before rapid-test positive).
“As in UK, there was a failure to test the high-risk persons who have been quarantined and who cannot/should not attend for round 2 mass screening which took place 8 days after round 1.”
Prof Sian Taylor-Phillips, Professor of Population Health, University of Warwick, said:
“The study found that after lockdown in Slovakia the numbers of recorded infections dropped and hospitalisations levelled off. Mass testing was given in combination with lockdown, but the authors did not know whether it made any contribution, because areas received both lockdown and mass testing. This is similar to the initial data from Liverpool, where all areas with lockdown decreased their number of infections, and this decrease appears to be similar in areas with and without mass testing. There are lots of things that can affect rate of infections so it’s very hard to interpret these findings.
“In this study from Slovakia people who tested positive on mass testing did not receive a PCR test to confirm whether they did or did not have coronavirus, so we do not know how many people were detected by the mass testing, or how accurate the test was.
“The data from Slovakia shows a drop in recorded infections within 1 week. If mass testing was working as expected, we might expect to see an immediate increase in recorded infections, as asymptomatic people are detected and add to the count. This doesn’t happen in Slovakia, which might be because people testing positive on mass testing don’t get a confirmatory test, and so would be removed from the count of infections as they are unconfirmed. So the drop in infections may have been partly due to changing the method of counting. Some more information is needed in addition to the information in current preprint to understand how much of an issue this is.”
Prof Igor Rudan, Joint Director of the Centre for Global Health and WHO Collaborating Centre, University of Edinburgh, said:
“There were several innovations during this pandemic that will now make it into epidemiology textbooks. The first one was the idea of mass-quarantine that was introduced to 56 million people in and around Wuhan, and then followed by many nations world-wide. However, national lockdowns are very blunt instruments that everyone tried to avoid ever since the first wave passed.
“One truly interesting innovation that Slovakia tried out to avoid a full national lockdown as a response to the intense second wave of the pandemic COVID-19 in Europe was a mass-testing of its entire adult population at two points in time. This enabled them to understand in real-time who is infected and who is not, and to separate those infected and their contacts from everyone else.
“This paper shows that the approach has been very successful, no matter through which lens it is observed. Prevalence of detected infections decreased by 58% within one week in the 45 counties that were subject to two rounds of mass testing. After some important adjustment for epidemiological context, it grew to 61%. Moreover, against a scenario of unmitigated growth, it increased to as much as 70%.
“This means that Slovakia’s mass testing approach showed large effectiveness independently of the other measures that were introduced and it also made a massive difference in comparison to the scenario if no measures were implemented. The concerns over the validity of rapid tests did not seem to undermine the impact of this measure or to cause much harm, as some feared. Clearly, mass population testing could become a new and more elegant way to deal with large and intense waves of pandemic of an unknown virus than a massive lockdown. This new epidemiological knowledge may lead to voluntary mass testing being offered at major cities world-wide, as the positive example of Liverpool in the UK has recently shown.
“Some may not feel that such mass testing was worth the effort, or cost. However, many interesting new approaches have been tested during COVID-19 pandemic in trying to address the problems that it has caused. Each time something new is being tried out, it provides a valuable lesson to other countries. This is why some things are worth trying so that we can learn of their effects, as long as countries can afford it and they do no harm to population health. We will likely have further pandemics in the future, so these lessons may even be valuable for some future application. I think was an interesting example that could find its application in major cities of Europe and the World, and possibly in whole countries where they can afford it.”
Dr Alexander Edwards, Associate Professor in Biomedical Technology, Reading School of Pharmacy, University of Reading, said:
“It’s great to see assessment of mass-testing programs, but it’s not straightforward to interpret this preprint in terms of suggesting mass-testing will work everywhere, nor will it be straightforward to work out how similar programs could be used in the UK. As is pointed out by the authors, there is a lot going on at the same time, so attributing a fall in cases to mass testing alone is hard. Nevertheless it includes some indication that a mass testing program can contribute to a reduction in cases.
“What is vital for any mass-testing program, is to understand all the steps that together must be achieved, and get these all right. I would expect many layers needed for mass testing to be successful: public health messages to get people to spend their time getting tested; effective tracking of all positive tests, and confirming if they are true positive cases; supporting anyone testing positive so they understand the result and are able to isolate (e.g. income support if they aren’t able to work from home); contact tracing with all true positives (and again support to isolate effectively); proper messaging to participants so that they understand test accuracy. For example, even if they receive a negative result, this doesn’t mean they are necessarily ‘safe’ as they could be incubating an infection, or the test might have been a false negative. Ideally, a cost-benefit assessment would be helpful, to work out the relative cost of mass testing vs other testing protocols or different interventions. Local factors must be considered, such as considering accessibility to testing centres, which will differ greatly (e.g. urban vs rural areas).
“All tests must be used as part of a wider, coherent public health strategy, that can make full consideration of accuracy and usefulness.”
Preprint (not a paper): ‘The effectiveness of population-wide, rapid antigen test based screening in reducing SARS-CoV-2 infection prevalence in Slovakia’ by Pavelka et al. was posted online on 4 December 2020. This work is not peer-reviewed.
All our previous output on this subject can be seen at this weblink: