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When Are People With Covid-19 Contagious?

by Coffee Table Science

Researchers at the Imperial College, London, have discovered a new timeline for people infected with coronavirus to determine how long these people are infectious and when they can be released from isolation. The study reveals how long infections can last in infected individuals after they are exposed to SARS-CoV-2 and how infectious they are to the community. The results suggest that most people who show symptoms are not infectious before the symptoms develop. However, two-thirds of patients can be contagious even after five days (current isolation period for covid) of showing covid symptoms. 

Image Credits: Pixabay

How did researchers find this? 

The study focussed on people (vaccinated and non-vaccinated) who were in contact with someone having a positive PCR test report in their home. They were questioned about developing symptoms. Their nasal and throat swabs were sent to laboratories for PCR and other testing procedures to determine the type and strength of the virus. The duration of infectiousness was measured in 42 people. Out of this, three people were asymptomatic (showed no symptoms), and 38 people reported a confirmed date of developing symptoms.

So, when are people infectious?

The researchers found that the average time until people were infectious, was five days. Although 24 out of 38 people had positive PCR reports, this does not indicate infectiousness as most people develop symptoms before becoming infectious, they said. Further, they reported that 8 of 34 cases shed the virus after seven days while the rest 22 shed the virus after five days of starting symptoms. These outcomes show that infected people should avoid contact with others and stay in quarantine (self-isolation) for at least five days.

Image Credits: Pixabay

What protocols are followed around the globe to curb covid transmission?

The government of every country has set protocols, including self-isolation, social distancing, and quarantine, to control covid infection. According to the CDC (Centre for Disease Control and Prevention), an infected person, whether symptomatic or asymptomatic, should be isolated for five days, followed by wearing a mask for five days around others. Further, WHO (World Health Organisation) has suggested some tips to minimise the risk of developing an infection. 

When to leave isolation?

To know the ideal time for leaving isolation, researchers analysed the infectiousness levels with the lateral flow test (a type of diagnostic procedure for covid) results. Based on the outcomes, researchers suggest that infected people can isolate for five days after symptoms appear and then go for the lateral flow test on the sixth day. If the test results are negative, they can leave isolation. However, if they continuously test positive or do not have access to lateral flow tests can leave on the tenth day to reduce transmission probabilities. 

The study did not analyse Omicron variants as some evidence suggests that they have low viral loads meaning that their amount in the body is less, and patients can be treated accordingly. Researchers stated that their recommendations may be dangerous but can be followed if the above is true. Overall, it can be said that an affected individual’s infectiousness plays a significant role in virus transmission with the environment and behavioural factors such as people interacting with the community. 

The study was published in the journal The Lancet Respiratory Medicine

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