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Home testing is ‘single most powerful tool' in reducing COVID transmission’

Mass home use of self-administered lateral flow tests have been “the single most powerful tool in reducing transmission of the virus,” says Prof Irene Petersen, head of epidemiology at University College London, in a BBC News report, commenting on a University of Liverpool analysis.

The idea of population-wide COVID testing on this scale was first revealed in leaked UK government documents in 2020. The plan was to use millions of cheap, throwaway lateral flow tests that could give a result in 15 minutes, rather than the more sensitive PCR tests that had to be sent off and processed in a laboratory.

But Operation Moonshot, as it was called by the government, got off to a bumpy start. There was alarm about the rumoured £100bn price tag, while some of the early results of a large pilot in Liverpool raised questions about the accuracy of the tests themselves.

When twice-weekly rapid testing was rolled out in secondary schools in the spring of 2021, there were worries that large numbers of pupils would be incorrectly told they had the virus, a so-called “false positive”, and sent home. Some scientists said the school programme could do “more harm than good” and leaked emails claimed it could all be scaled back.

But data now suggest much of that concern was misplaced. Since March 2021, 183,939 pupils in England have tested positive on a lateral flow test at home and then had a sample sent off to a laboratory for a follow-up PCR test. In total 89% of those swabs returned the same positive result.

BBC News reports that the proportion of false positives does increase when the prevalence of the disease falls in society. But the weekly rate of those positive lateral flow tests later confirmed by PCR has never fallen below 50% and has been above 84% since the start of the school year in September.

Alexander Edwards, associate professor in biomedical technology at the University of Reading, says it “quickly became clear” that if the tests were used as instructed, “you don’t tend to get large numbers of false positives”.

Those same rapid lateral flow tests have become part of everyday life. Initially they were rolled out in healthcare settings, workplaces and sporting events. Then last April, the programme was extended to the general public. Boxes of seven tests could be delivered free, or picked up from a pharmacy.

But false positives are not the only possible drawback with mass testing on this scale. Some scientists are concerned that the public are often far too trusting if their lateral flow test comes back negative.

“It is absolutely not a get-out-of-jail free card, and you need to continue to take precautions, like mask wearing and social distancing,” said Prof Sheila Bird from the MRC Biostatistics Unit at the University of Cambridge. “It is helping to weed out some, but certainly not all, of the true positives.”

An analysis of the lateral flow kit used in Liverpool showed it only detected around half of people without symptoms who, on the same day, returned a positive PCR result. But those PCRs can pick up old genetic material from the virus left in the body even after the infectious period. Prof Petersen says that rapid lateral flow tests are far better at spotting the cases most likely to pass COVID on to someone else.

Quite how well lateral flow kits perform against Omicron is still unclear. Experiments showed the main brands used in the UK did successfully detect all 15 of the samples infected with the new variant. But a small study published in the past week, and based on different kits used in the US, raised fresh concerns – finding that some Omicron cases could be infectious for several days before being detected by rapid tests using nasal swabs.

Was it worth it?

Health authorities budgeted £4.7bn this financial year for mass testing in England with the bulk of that going to suppliers of the kits, most of which are manufactured in China. Whether all that money is worth it is something epidemiologists are likely to be arguing about for many years, writes BBC News. Untangling the effects of rapid testing from all the other COVID measures, from mask wearing to self-isolation, is extremely difficult and open to some interpretation.

A recent analysis of the first Liverpool pilot, which has not yet been peer reviewed by other scientists, found that the early roll out of mass testing in the city was linked to a 32% fall in COVID hospital admissions, and relieved significant pressure on the NHS. Parts of that first pilot scheme have now become government policy, for example using daily rapid tests as an alternative to quarantine for some people.

Some scientists would like to see ministers go further and use lateral flows to completely replace expensive PCR lab tests, both for those with and without COVID symptoms.

“The PCR programme is such a complete waste of resources. It’s there because it was the only thing we had at the beginning. It should be phased out sooner rather than later,” says Prof Irene Petersen at UCL.

Others think that as the Omicron wave passes, it is time to wind down the mass testing programme completely. Allyson Pollock, professor of public health at Newcastle University, says tests should be part of a clinical diagnosis or targeted at places like care homes and hospitals, where people work with vulnerable groups.

“The cost of mass testing has been staggering,” she says. “The best advice is if you have symptoms is to simply stay at home until you are better, and that way you will avoid spreading COVID, flu and a host of other viral infections.

“All tests create harms. Tests can give false reassurance on the one hand, and on the other can create false alarms and unnecessary isolation.”

Liverpool Covid-SMART pilot evaluation

A team of experts led by the University of Liverpool evaluated the world’s first city-wide, voluntary COVID-19 rapid antigen testing pilot in Liverpool from November 2020, followed by early roll-out across the wider Liverpool City Region in December 2020 of the national COVID-19 community testing scheme.

Quantitative evaluation, Liverpool City Region community testing roll out:

The latest analysis of Liverpool City Region’s Covid-SMART community testing initiative (December 2020 – July 2021) reveals insights that will help policymakers, public health teams and the public with community approaches to COVID-19 testing.

The evaluation report, led by researchers from the University of Liverpool’s Institute of Population Health, identified:

A 32% reduction in COVID-19 hospitalisations – a larger effect than previously reported from synthetic control analysis following release of more detailed national data.
The ‘test to release’ scheme saved 8,292 key worker workdays. Workers used a daily negative lateral flow test (LFT) as a COVID-19 certification to work. 34 COVID-19 cases were identified – only three of these had been missed by daily LFTs.
Test-to-release (also known as daily contact testing) is important for civic resilience – evidence needs to inform current and locally variable policies.

Main findings
The pilot team developed a SMART (systematic, meaningful, asymptomatic and agile, repeated testing) approach. The targets were:

· test-to-protect (vulnerable individuals, settings and services)

· test-to-release (sooner from quarantine, when appropriate and combined with other measures)

· test-to-enable (safer return to key activities for social fabric and the economy, when appropriate and combined with other measures)

The evaluation found that a low-cost, rapid, no-lab test of likely infectiousness saves time and extends the reach of health protection measures. The data showed that lateral flow rapid antigen testing meets this need when coordinated by an effective local public health service. The end-to-end testing service was found valuable and has been continued beyond the pilot as a core part of Liverpool's COVID-19 response.

 

BBC News article – Look familiar? How rapid tests changed the pandemic (Open access)

 

Liverpool Unversity COVID SMART rapid antigen community testing (Open access)

 

See more from MedicalBrief archives:

 

Rapid antigen test found more effective than PCR assay — Large US study

 

UK regulator gives go-ahead to 20-second COVID-19 test

 

New device accurately diagnoses COVID-19 from saliva samples

 

 

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