As set out in the government’s Roadmap, our national journey out of lockdown is reliant on us being able to control variants of concern.
To increase our preparedness and heighten our defences against new variants, we have backed new technology, known ‘genotype assay testing’, which could halve the time it takes to identify if a positive COVID-19 test contains a variant of concern. This will allow positive cases to be traced sooner and stop the spread of variants on UK soil.
Genotype assay testing is compatible only with PCR tests and in order to detect the maximum number of cases with variants, the government is reintroducing confirmatory PCR testing for positive LFD test results in England. Confirmatory tests are used to validate the result of the initial rapid test.
The reintroduction of confirmatory testing will also bring domestic testing requirements in line with the strengthened regime in place for international arrivals. The heightened border controls, introduced in February, are already helping to reduce the possible spread of variants in the UK, with passengers required to quarantine when arriving from ‘red list’ locations and self-isolate at home when travelling from ‘amber list’ destinations.
Recent analysis by NHS Test and Trace shows lateral flow tests (LFD) have a specificity of at least 99.9%. This means that for every 1,000 lateral flow tests carried out, there is fewer than one false positive result.
Despite this, at times of low prevalence, the probability of a false positive from an LFD is higher, so we are mitigating this by asking people to confirm a positive LFD result with a PCR test.
Contact tracing will continue to be triggered by a positive LFD result in assisted settings, but will be stopped automatically after receipt of a negative confirmatory PCR test, if the PCR was taken within the 2 days following the positive LFD result. NHS Test and Trace has introduced new operational improvements that will automatically inform anyone self-isolating from a positive LFD and their contacts to stop isolating if the confirmatory PCR is taken within two days and is negative.
This means we can reintroduce confirmatory PCR for supervised testing without losing the benefits of rapid contact tracing, and freeing people and their contacts from self-isolation in the instance of a false positive.
It remains essential that anyone who gets a positive result from an LFD result self-isolates immediately, as must other members of their household, while they get a confirmatory PCR test.
In the coming weeks the NHS Covid19 app, which shows the outcome of a test result, will be able to overturn a positive LFD result if the result changes following a confirmatory PCR.