Coronavirus: COVID infectiousness lasts for more than 5 days, finds new study

A new research study has shed light on the duration of COVID infection and the time till which a person remains infectious. The study done by Imperial College London scientists provides an insight on how long people with COVID are actually infectious. "The study is the first real-world evidence of this kind," it says.

Omicron is currently the dominant strain of the virus that is driving the majority of the infection worldwide. India's active COVID caseload currently stands at 1,01,166 with a total of 13,272 new cases recorded in the last 24 hours.

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The new research study by the Imperial College London is about determining the infectious nature of the COVID infection with special emphasis on Omicron led infection which mostly shows mild symptoms.

The study is said to be the first to figure out how long infectiousness lasts in COVID infection. "The study team conducted detailed daily tests from when people were exposed to SARS-CoV-2 to look at how much infectious virus they were shedding throughout their infection," the study report says.

The study is based on 57 participants. "It may not apply to very young and old people, or those with medical conditions. This is because children are thought to clear the virus more quickly, while older people and those with medical conditions may be slower at clearing the virus," reads the research report.

The study found that of the total number of participants, two-thirds of cases were still infectious five days after their symptoms began, and one-quarter were still infectious at seven days.

It also found that only one in five participants were infectious before symptom onset, so most people only became infectious after they developed symptoms.

On the duration of the self isolation period, the researchers say, people can complete lateral flow tests on days six and seven and can leave isolation only if the tests are negative.

"If a person continues to test positive on day six or beyond, or does not have access to lateral flow tests, we think they should remain in isolation until they’ve had two consecutive days with negative test results," says study author, Professor Ajit Lalvani, Director of the NIHR Respiratory Infections Health Protection Research Unit at Imperial.

The participants were monitored in their homes from the day when they were first exposed to the virus, the day when they developed infection till the day they stopped showing signs of infection.

"By using special daily tests to measure infectious virus (not just PCR) and daily symptom records we were able to define the window in which people are infectious. This is fundamental to controlling any pandemic and has not been previously defined for any respiratory infection in the community,” says Professor Lalvani.

Participants completed daily questionnaires about their symptoms and did daily nasal and throat swabs that were sent to a laboratory for PCR-testing.

Though 57 participants had enrolled for the study, the duration of infectiousness was measured in 42 people due to several reasons like some of the participants did not share any information, and some did not shed culturable virus, the study says.

The study suggests that lateral flow tests do not detect the start of infectiousness well, they more accurately identify when someone is no longer infectious and can safely leave isolation.

The researchers carried out 652 lateral flow tests to determine its accuracy in comparison to PCR tests.

Lateral flow tests include taking samples from the throat and nose or nose only using a swab. Depending on the type of test, one can get the result within 10-30 minutes.

The infected individual's infectiousness is a big factor in COVID transmission. With the pandemic nowhere near over, it is important to know about the infectiousness and the duration of self isolation.

“Self-isolation is not necessary by law, but people who want to isolate need clear guidance on what to do. The NHS currently advises that if you test positive for COVID-19 you should try to stay at home and avoid contact with other people for five days, but our data suggest that under a crude five-day self-isolation period two-thirds of cases released into the community would still be infectious – though their level of infectiousness would have substantially reduced compared to earlier in the course of their infection,” says Professor Lalvani.

"We recommend that anyone who has been exposed to the virus and has symptoms isolates for five days, then uses daily lateral flow tests to safely leave isolation when two consecutive daily tests are negative," he suggests.