Researchers have made a new revelation about what happens when people get infected with COVID-19.
Among people who develop COVID-19 symptoms, most are not infectious before symptoms develop, but two-thirds of cases are still infectious five days after their symptoms begin, according to researchers from the Imperial College London.
“We closely monitored people in their homes from when they were first exposed to the virus, capturing the moment when they developed infection through until they ceased being infectious,” said Ajit Lalvani, the director of the NIHR Health Protection Research Unit in Respiratory Infections at Imperial.
“Combining our results with what we know about the dynamics of omicron infections, we believe that the duration of infectiousness we’ve observed is broadly generalizable to current COVID-19 variants, although their infectious window may be a bit shorter.”
The new study followed people who were exposed to someone with PCR-confirmed COVID-19 in their homes between September 2020 and March 2021 (pre-alpha COVID-19 virus and alpha variant waves) and May to October 2021 (delta variant wave), including some who were vaccinated and others who were not.
PCR-positive samples were then tested to determine whether they contained infectious virus and the infectiousness of the virus.
The researchers completed 652 lateral flow tests on the samples to determine how accurate lateral flow tests were at identifying actual infectiousness as opposed to PCR positivity.
Samples from a total of 57 people were used, but not all were included in some analyses because of some participants not sharing information about their symptoms, some not shedding culturable virus and some shedding infectious virus before or beyond the sampling period.
The study found that the overall median time that people were infectious was five days. Based on their findings, the researchers recommend that people with COVID-19 isolate for five days after symptoms begin, then complete lateral flow tests from the sixth day.
If these tests are negative two days in a row, it is safe to leave isolation.
If a person continues to test positive or does not have access to lateral flow devices, they should remain in isolation and, to minimize transmission to others, only leave on the 10th day after their symptoms began.
The study did not assess the omicron subvariants currently circulating. There is some evidence that the omicron variant has a lower viral load and shed for less time than other variants, and the researchers note that their recommendations may be cautious, but still applicable, if this is true.