A new study out of the U.K. has revealed most people who test positive for COVID-19 remain infectious after five days from their first sight of symptoms.
Researchers at Imperial College London followed a group of people who developed mild cases of COVID-19 to better understand when and for how long they remain infectious.
The study followed 57 people in various households who tested positive for COVID-19 and found two thirds of the participants remained infectious five days after their symptoms started showing. Additionally, one quarter were still infectious seven days after their initial symptoms.
Published in the peer-reviewed on Thursday, the study found one in five people were contagious before they started showing symptoms, suggesting the majority of those infected with COVID-19 are not likely to be infectious before symptoms develop.
The study group endured daily symptom reporting and tests, including both PCR and , more commonly known as rapid tests. Through this, the researchers found lateral flow tests are not reliable for detecting the start of infection, but can be useful in determining when to shorten the quarantine period.
鈥淥ur study finds that infectiousness usually begins soon after you develop COVID-19 symptoms. 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,鈥 said lead researcher Ajit Lalvani in a .
The study period took place between the pre-Alpha and Alpha variant waves in 2020 and Delta variant wave in 2021. While the study pre-dates the most recent wave of the Omicron variant and its sub-variants, the lead researchers say the length of infectiousness is likely similar as other variants.
Similar to the U.K., the majority of COVID-19 guidelines in Canada recommend people self-isolate for five days after showing symptoms, and can end their quarantine after five days if their symptoms don鈥檛 persist.
However, authors of the new study stress the importance of following self-isolation guidelines, regardless of whether they are mandated.
鈥淭here is no longer a legal requirement to self-isolate if you test positive for COVID-19 [in the U.K.] but most people still want to isolate until they are not infectious,鈥 co-author Seran Hakki said in the release.
鈥淥ur study is the first to assess how long infectiousness lasts for, using real life evidence from naturally acquired infection. Our findings can thus inform guidance as to how to safely end self-isolation.鈥
