Widespread use of lateral flow tests in UK (CW3.1)

As of 9 April, everyone in the UK will be able to take a free rapid coronavirus test twice a week (more). This is the next wave in the expansion of COVID testing that previously focused on front line healthcare workers, care home residents and staff, those that need to travel to work and secondary school pupils. This is despite the UK already being the most tested country in the G8. Figure 1.1 provides a dramatic comparison of the change in positivity rates since the beginning of the year across the G8 countries (more).

Figure 1.1 – Trends in positivity rates for G8 countries

Source: OurWorldInData

There are particular concerns about the sensitivity of the lateral flow devices (LFD) and their ability to detect asymptomatic infections. The most recent data released by NHS Test and Trace indicates that there were 5,486,756 LFD tests over the period 25-31 March (more), of which 8,374 were positive, or a positivity rate of 0.15%. In total, NHS Test and Trace reports that there have been 130,000 positive cases from LFD tests that would have otherwise been missed – “breaking the chain of infection”.

Comparative information for PCR testing over the period 25-31 March includes 996,728 tests, of which 2.0% were positive. That said, PCR testing would be focused on those individuals with symptoms or for confirmatory purposes.

There are other countries with comparable numbers of tests per positive case, such as Australia - 979 per 1 million in week to 11 April (more) - but such countries typically have suppression strategies designed to prevent any outbreaks, which the UK is a long way away from achieving. The question is whether a further massive expansion of LFD testing is the best use of available resources.

As far as I am aware, no other country has proposed to provide blanket and unfocused testing across the population at a cost running into hundreds of £m each week. Particularly when many positive tests may go unreported because of lack of financial support for those testing positive and inability to check results, and when poor technique and low sensitivity of LFD may mean that a worrying number of false negatives would be confident that they could circulate as the country unlocks.

A number of experts, including Professor Stephen Relcher who advises on behavioural science on the SPI-B subcommittee of SAGE, have questioned whether any benefits will be seen in public health from this policy, and wonder why no cost-benefit analyses have been presented from appropriately designed evaluation studies (more).

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