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Routine tests on sewage can act as an early warning system for outbreaks of dangerous variants of coronavirus as vaccines are rolled out across the country, government scientists have concluded.

Tests on sewage samples collected in London from January 2020 tracked the rise and fall of coronavirus infections through successive waves and lockdowns and detected the more transmissible Kent variant before it was known to Public Health England.

Researchers at the National Institute for Biological Standards and Control (NIBSC) said the findings show how the tests can provide an “early warning” that troubling variants, such as those first spotted in South Africa and Brazil, are spreading in the UK.

Because sewage tests look for the virus in the waste of thousands to millions of people at once, they can potentially reveal outbreaks faster than lab-based tests which rely on people to develop symptoms, come forward for a test, and have their results logged by NHS test and trace.

The scientists looked for coronavirus RNA – its genetic code – in samples collected from the inlet pipe of a major London sewage plant between January 2020 to January 2021. No sign of coronavirus was detected in the first sample in January, but low levels were found in February, days before the first cases were confirmed in the capital.

Levels of the virus in London sewage rose in the 2020 spring wave, fell sharply with the first nationwide lockdown from the end of March, and remained low until early September, when they began to climb again. The first evidence for the more transmissible Kent variant, named B117, was spotted in a sewage sample from early November, when Public Health England were still investigating why infections in Kent had failed to come down despite the November lockdown.

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According to the findings, which have yet to be peer reviewed, further sewage samples showed how the Kent variant rapidly became dominant in London, accounting for only 8% of positive samples on 10 November but a staggering 97% on 26 January.

The variants first spotted in South Africa (B1351) and Brazil (P1) are particularly concerning because they contain a mutation called E484K which appears to confer partial resistance to antibodies people gain from vaccination or previous infection in the first wave. Surveillance has since picked up the same mutation in samples of the Kent variant in Bristol and another variant circulating in the north-west.



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