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Asymptomatic Testing Key to Pandemic Preparedness

COVID-19 infections that would have been missed were detected through asymptomatic PCR testing for NHS staff, a blueprint for future NHS–academic partnerships to follow, said experts.

An important component of the UK's early response to the COVID-19 pandemic was increasing SARS-CoV-2 testing capacity across the NHS, pointed out the authors of a new research letter, "Independent SARS-CoV-2 testing protected NHS hospitals and care homes in Northwest London", published in The Lancet

"Estimates of true asymptomatic infections vary, but up to 40% of all COVID-19 infections might be asymptomatic," they warned.

Regular asymptomatic testing for COVID-19 was paused by the Government at the end of August last year, in response to cases continuing to fall. Settings where asymptomatic testing of staff and patients or residents was paused included the NHS, and adult social care, and hospice services.

Significant Number of Additional Infections Identified

In the new observational study of testing data from the Crick COVID Testing Pipeline, researchers examined test positivity rates across different NHS trusts with a view to understanding both the effect of hospital trust screening policies, and the Institute's in-person work policy, to inform future pandemic planning. 

The pipeline – created when the Francis Crick Institute repurposed its laboratory facilities in partnership with University College London Hospitals (UCLH) and the Health Services Laboratory – provided both asymptomatic screening and SARS-CoV-2 diagnostic testing for staff in eight NHS trusts and 98 local care homes and rehabilitation facilities, covering London boroughs with high rates of COVID-19, that included Brent, Harrow, Barnet, and Ealing.

To enable essential research work at the Institute to continue, as well as support the Crick Vaccination Centre, testing was then expanded to its staff.

The researchers found that 7316 positive infections were detected from 680,602 tests (1%) between 1 April 2020 and 14 April 2022. Moreover, the authors pointed out that they had captured variants of concern often "ahead of their designation by WHO" – alpha (B.1.1.7) was first detected 33 days before, delta (B.1.617.2) 27 days before, and omicron (BA.1) 5 days following its designation, they alerted.

The researchers also found that from the tests run, just over 2 out of 5 (40.8%) of all positive tests were from UCLH and The Royal Marsden NHS Foundation Trust, both of whom offered staff and patients asymptomatic testing.

"This high incidence suggested a significant number of additional infections were being detected by this strategy," commented the authors.

"Our analysis suggests that asymptomatic testing was responsible for capturing a significant number of infections that would have otherwise been missed, and could have spread to more NHS staff and their patients," emphasised Chris Bailey, clinical fellow at the Francis Crick Institute and author of the study.

Blueprint For Future Pandemic Response

The researchers next adjusted for organisation size and calculated (by dividing the daily incidence of positive tests for each site, divided by the daily incidence estimates for London's population) an incidence rate ratio for each site over the first 4 months of testing. They found that the incidence of cases at the NHS sites that offered primarily asymptomatic testing were up to 13 times that of the London population at the time.

The strategy also helped to keep overall numbers lower in the workplace, the authors said, after having compared infection data from staff at the Institute, where they observed that peaks of infection were flatter than within the Institute's local borough of Camden.

Whilst the authors recognised that their study was restricted by its observational design, the data suggested that, not only were asymptomatic testing strategies responsible for uncovering sizeable number of additional infections, this was achieved particularly in the "early phase" of the pandemic, they underlined.

"Our work highlights the importance of prioritising testing – including regular asymptomatic testing of key workers, including NHS and care home staff – during the first phase of the pandemic response," stressed the authors.

Dr Emma Wall, an infectious diseases consultant at UCLH and senior clinical research fellow for the Legacy study, urged that the data gathered throughout the pandemic needed to be "put to good use". She emphasised that the repurposing of lab facilities and partnering with local NHS trusts, as the Crick had done, was a useful "blueprint" for future NHS-academic partnerships to follow, that could be "rapidly set up" in the event of another pandemic.

This research was funded in whole, or in part, by the Wellcome Trust. TS is supported by a Sir Henry Wellcome Postdoctoral Fellowship from the Wellcome Trust. Unrelated to this correspondence, CSw reports grants from BMS, Ono-Pharmaceuticals, Boehringer Ingelheim, Roche-Ventana, Pfizer, and Archer Dx; personal fees from Genentech, Sarah Canon Research Institute, Medicxi, Metabomed, Bicycle Therapeutics, GRAIL, Amgen, AstraZeneca, BMS, Illumina, GlaxoSmithKline, MSD, and Roche-Ventana; and stock options from Apogen Biotech, Epic Biosciences, GRAIL, Achilles Therapeutics, and Bicycle Therapeutics.