Covid rapid tests are more accurate than thought, according to a Harvard epidemiologist.
There has been conflicting data on the efficacy of rapid tests which aim to confirm or rule out whether a person has coronavirus.
Dr Michael Mina, an epidemiologist at Harvard Public Health, argues that the tests are “erroneously citied as not sensitive enough” when in fact they are more effective than some people think.
This is because they are often compared with PCR tests which still produce a positive result even after people are no longer infectious, he explains.
“Rapid tests have the same accuracy in asymptomatics as symptomatics,” the assistant professor said on Twitter.
“If someone says they are less sensitive to detect infectious people who are asymptomatic, they are wrong.
“The test does not care about your symptoms, it cares about how much virus you have.”
PCR tests stay positive “so long” that the Centers for Disease Control and Prevention in the United States recommends no retest for 90 days, Dr Mina highlighted.
The test, which involves taking a swab of the inside of your nose and the back of your throat using a long cotton bud, remains positive for weeks even though infectiousness only lasts up to seven days, he said.
“Thus rapid tests are only positive for three to seven days or about 30 per cent of the time that people are PCR positive,” he added.
“Without symptoms, it’s a random sample along the PCR positive timeline and thus looks like rapid tests miss 70 per cent. Even if they were to detect 100 per cent of contagious people.”
Regular rapid testing has become an essential part of the UK’s aim to break the chain of transmission, alongside the vaccine rollout and current guidelines.
The government advises for everybody over the age of 18 who does not have Covid symptoms to take a rapid test twice a week.
These lateral flow tests can quickly identify the presence of Covid antigens or proteins and are less expensive than a PCR.
They comprise of a handheld device with an absorbent pad at one end and a strip of test paper at the other which changes colour when a person is positive.
Results take 15 to 30 minutes and tests do not need to be sent to a lab.