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The government has now released some info on how LFTs compared to PCR in field tests in Liverpool. h/t @ScienceShared
It's not great.
LFTs found about half the people that tested positive with PCR. Which is a little better than my back of the envelope estimate.
But...
It's not great.
LFTs found about half the people that tested positive with PCR. Which is a little better than my back of the envelope estimate.
But...
It only found "more than" 70% of people "with higher viral loads, who are likely to be the most infectious".
Far less than the 95% it managed in the original Porton Down trial, which was in a lab using spiked samples, not members of the public shoving swabs up their noses.
Far less than the 95% it managed in the original Porton Down trial, which was in a lab using spiked samples, not members of the public shoving swabs up their noses.
So although the LFTs have found a few hundred cases that would have been missed otherwise, they still missed half the people with the virus that were tested.
Including 20-30% of the ones most likely to be infectious.
Source: Community testing prospectus
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/939957/Community_rapid_testing_prospectus_FINAL_30-11.pdf
Including 20-30% of the ones most likely to be infectious.
Source: Community testing prospectus
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/939957/Community_rapid_testing_prospectus_FINAL_30-11.pdf
Meanwhile the "prospectus", which reads like a sales pitch, claims "pilots .. in Liverpool and Merthyr Tydfil are showing positive impact".
As noted earlier, cases were already falling in Liverpool before the trial began and don't seem to be falling noticeably faster now.
As noted earlier, cases were already falling in Liverpool before the trial began and don't seem to be falling noticeably faster now.
And the "prospectus" has to admit the MHRA hasn't actually approved LFTs for community testing yet, and that they're not designed for mass testing of asymptomatic people using self-swabbing.
DHSC says it's in "ongoing and constructive dialogue" with the MHRA about this.
DHSC says it's in "ongoing and constructive dialogue" with the MHRA about this.
Despite all this, the government says "community testing .. may enable areas to move down through the tiers".
Dangling a possibly unrealistic carrot in front of local authorities representing the millions of people still facing the toughest restrictions as lockdown ends.
Dangling a possibly unrealistic carrot in front of local authorities representing the millions of people still facing the toughest restrictions as lockdown ends.
There's even a plan to let people in tier 3 areas go to live performances and sports events, although that at least requires TWO negative tests.
But if each test only has a 50:50 chance of detecting the virus, it's still far from foolproof.
But if each test only has a 50:50 chance of detecting the virus, it's still far from foolproof.
All of which raises concerns about how and why the tests are being fast tracked before the full data from Liverpool has been published.
And whether the tests are sensitive enough when used this way to avoid giving people a false sense of security.
And whether the tests are sensitive enough when used this way to avoid giving people a false sense of security.
