Millions of people around the world have recovered from Covid-19, and one of their primary concerns is whether they can get re-infected by the novel coronavirus. Have they developed immunity, and if so, for how long? There have been a few instances of people who have been declared recovered, testing positive again, raising fears of re-infection.
As of now, scientists are unable to say whether re-infection is possible, and if so, after how much time. They are also unsure whether an infected person becomes immune to re-infection. A new guidance from the Centers of Disease Control and Prevention (CDC) in the United States attempts to answer some of these questions in light of updated knowledge from latest research. Read in Tamil
What is the CDC guidance?
In the guidance, issued during the weekend, the CDC, which is part of US Department of Health, said no confirmed case of re-infection had been detected till now.
“Reinfection with SARS-CoV-2 has not yet been definitively confirmed in any recovered persons to date. If, and if so when, persons can be reinfected with the SARS-CoV-2 remains unknown, and is a subject of investigation,” the CDC said.
However, this does not mean that people once infected with the virus can be said to have developed an immunity against re-infection.
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What about recovered patients who have tested positive again?
The CDC said recovered patient can have low levels of virus in their bodies for up to three months after they were first diagnosed, and this can be detected in the diagnostic tests. This is the reason why there have been instances of recovered people having tested positive again within the three-month period. But such people do not transmit the virus to others, the CDC said.
Therefore, retesting a person within the three month period was “unnecessary”. Even if they test positive, it most probably would be because of leftover traces of virus (“persistent shedding”) rather than a case of re-infection.
“Recovered persons can continue to shed detectable SARS-CoV-2 RNA in upper respiratory specimens for up to three months after illness onset, albeit at concentrations considerably lower than during illness, in ranges where replication-competent virus (those that can replicate and spread) has not been reliably recovered and infectiousness is unlikely. The etiology (cause of the disease) of this persistently detectable SARS-CoV-2 RNA has yet to be determined,” it said.
“Studies have not found evidence that clinically recovered persons with persistence of viral RNA have transmitted SARS-CoV-2 to others,” it said.
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What else do the guidelines say?
The CDC said that persons with mild to moderate symptoms can be released from isolation 10 days after the they were first tested positive, while those with severe symptoms need to be kept in isolation for a maximum of 20 days.
“Available data indicate that persons with mild to moderate COVID-19 remain infectious no longer than 10 days after symptom onset. Persons with more severe to critical illness or severe immunocompromise likely remain infectious no longer than 20 days after symptom onset,” it said.
The CDC said its new recommendations were based on more than 15 international and US-based published studies that looked at the length of infection, duration of viral shed, asymptomatic spread, and the risk of spread among various patient groups.
“Researchers have found that the amount of live virus in the nose and throat drops significantly soon after the COVID19 symptoms develop. Additionally, the duration of infectiousness in most people with COVID19 is no longer than 10 days after symptoms begin, and no longer than 20 days in people with severe illness…,” it said.
It said the latest findings strengthened the case for relying on “symptom-based, rather than test-based strategy for ending isolation” of infected patients, so that persons who are “by current evidence no longer infectious are not kept unnecessarily isolated and excluded from work or other responsibilities”.
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