Once obscure diagnostic devices, lateral flow tests have had a rocky path to mainstream use, but some experts think their rise to ubiquity is a "heroic" step in the fight against Covid-19.
The first wave of Covid crashed in early 2020 and governments scrambled to secure PPE, ventilators and reagents for laboratory testing, behind the scenes some had already foreseen a role for the pregnancy test-style kits.
David Campbell, the director of the Derby-based diagnostics company Surescreen, said that they started thinking about it in late 2019. We did a lot of work on Mers. Initially, we thought it would be a niche product.
The first Covid tests were designed to detect antibodies. Governments at the time hoped that proof of prior infections would allow people to return to their normal lives.
By April 2020 the UK government had announced the purchase of 17.5m lateral flow testing kits. This was a mistake. Prof Sir John Bell, professor of medicine at Oxford University, said that they were awful. He noted that Surescreen's test was not included. There were a lot of people trying to sell tests that didn't work. It was scandalous. That was the beginning of the tests.
Bell said that one valuable lesson was the need for a robust validation process. Bell chaired a group of Porton Down scientists who were tasked with testing tests for use.
By autumn 2020 many companies had switched their focus to antigen tests, which use synthetic antibodies to detect the virus itself. The UK government moved on to another project, called Operation Moonshot, which was supposed to deliver millions of these kits to people's homes. Bell said that whenever he hears the word "moonshot" from No 10 his heart sinks. The reality is that the tests have been delivered. It has been one of the more heroic moments of the epidemic.
There is a sign in the window of a store. There is a photograph of Maureen McLean.
The government fast-tracked a pilot of community testing of about 125,000 people in a single city, and found that 897 people who did not know they had the virus were stopped from spreading it further. The tests in the field missed infections in people who were self-swabbing and in people with high viral loads.
A vocal group of scientists warned that reliance on LFTs to open up schools and the economy risked giving false reassurance.
Prof Iain Buchan, chair in public health and clinical informatics at the University ofLiverpool, said that they were being attacked left, right and centre. It was almost a religious argument about whether or not to do the test. We received death threats.
People saw things differently. He said that those who were criticising it were seeing it as a diagnostic tool. He and others argued that the tests were not comparable to the gold standard of laboratory-based tests. The aim of the Lateral flow tests was to find people who would never have come forward for a test in the first place and give them results in minutes rather than days.
The use of flow tests reduced the number of hospital admissions in the second wave. He said that the reduction could not have been solely the result of people who tested positive for self-isolating, but that it was the result of other household members behaving more cautiously.
Evidence shows that LFTs are more sensitive when people have a high viral load, which has led some to argue that they are a better test of when people are actually infectious. There is no established threshold for infectiousness and the sensitivity to low levels of antigens varies between different brands of test.
The ability of LFTs to detect people while they are infectious seems to have become accepted dogma, but we know from our latest review that there is considerable variation.
The volunteers handed out boxes of tests. Tolga Akmen is pictured.
False positives were delivered by the lateral flow tests as case numbers fell. If you test positive, the chances that you have Covid depend on the quality of the test and the current prevalence of the virus. If an LFT delivers a false positive result for one in 1,000 tests, the chances of someone with a positive result are only 50%. If the prevalence is one in 10 people, that person can be 99% sure they are not infectious.
The latter is the most likely explanation for why the tests have come into their own. Since the emergence of Omicron, case numbers in the UK have risen to such extraordinary levels that the issue of people having to isolated unnecessarily due to false positive results is negligible. The risk of severe disease has been lessened by vaccinations. We are still facing a disease that needs to be brought under control. The UK is performing a huge public health trial on the extent to which mass testing can achieve this goal.
The way in which the tests have changed from being used to diagnose Covid-19 to being used for daily use in people without symptoms is quite the story. There is no published evidence from primary studies that fully supports this policy.
The jury is not sure if government advice to "flow before you go" will be remembered as another episode of the Pandemic, or if it will become part of the fabric of daily life. Mass testing will be less valuable as case rates go down. Others think that the Pandemic will lead to a wider range of respiratory viruses. In the future, they say, parents might do a quick test on their child before sending them to school when they wake up with a slight cough, or an elderly person might test for flu and take antiviral tablets before the symptoms really kick in.
Bell said that these could change the impact of respiratory viruses in society.
