Scientists investigate why some test positive for Covid-19 twice – The Wall Street Journal

The world is unlikely to be able to shake off the Covid-19 pandemic until many of us are immune to the deadly virus – either through vaccination or infection. This nasty virus is so new and unusual it's not even clear yet whether people who have contracted the disease can build up sufficient immunity to protect against a subsequent infection. As The Wall Street Journal points out, a laboratory test on monkeys suggests that there is optimism to believe that immunity can build with the spread of the disease. But it's still early days in the research, with concern about the presence of Covid-19 testing positive in people long after they appear to have recovered. – Jackie Cameron___STEADY_PAYWALL___.Can you get Covid-19 twice?.By Preetika Rana(The Wall Street Journal) – More than 160 South Koreans tested positive a second time for the novel coronavirus last month, weeks after being discharged from medical supervision. Some symptom-free Americans have been barred from donating their blood plasma to help treat others because they are still testing positive.The revelations are generating concern that people who have had Covid-19 are getting infected anew – something scientists say current evidence doesn't support.Here is what we know, and don't know, about the possibility of becoming sick with the virus more than once.I recently recovered from Covid-19. Does that mean I can't get it again?Most scientists say that people who have had Covid-19 gain some immunity to the virus that causes it. What they don't know is whether that protection lasts a few months, a few years or a lifetime.What factors affect immunity?The immune system wards off infections by producing antibodies that fight invaders. A range of hereditary and environmental factors, including diet and sleep patterns, typically affect the strength and longevity of those defenses.Immunity also depends on the pathogen. For example, infection by the virus that causes measles confers lifelong immunity. Others, like the influenza virus, can mutate so rapidly that protective antibodies might not recognise them during a reinfection.The novel coronavirus mutates more slowly than the influenza virus. That gives researchers hope that any natural immunity, or vaccine, would offer more lasting protection. Even if someone gets sick again, researchers believe a second infection might be milder than the first.How soon would my body produce antibodies to fight the novel coronavirus after an initial infection?Data are scant, but preliminary research shows antibodies can emerge within days or several weeks of the onset of symptoms. A study involving 34 hospitalised cases in China found that two patients, both in their 80s, produced antibodies within three days of symptom onset. The rest produced them two weeks after symptoms first surfaced.The findings were vetted by other experts and published in an academic journal in March.Is there any good news?A group of Chinese researchers reported in March that they had infected four rhesus macaques, allowed them to recover and then tried to reinfect two of them with the same strain of the virus. Neither became sick again.Then why are some people testing positive again?South Korean health officials are refraining from labelling them as "reinfections." Korean doctors involved in a continuing government review believe that those patients likely harboured low levels of the virus that diagnostic polymerase chain reaction, or PCR, tests failed to pick up. In later stages of the disease, the virus settles into the lungs where it can elude detection. The virus, they say, hadn't been fully cleared from the body.John Brooks, the chief medical officer for the US Centres for Disease Control and Prevention's Covid-19 response says the agency is monitoring whether the pattern repeats itself in the US.How do I know I've fully recovered?Clinicians have mixed views on what constitutes recovery because long-term data aren't yet available. Guidelines vary across the globe, and even within countries. In a peer-reviewed study published last month, researchers in Hong Kong detected the virus in the faeces of Covid-19 survivors even as their respiratory samples tested negative. Viral fragments can linger in the body after symptoms disappear, but it doesn't mean that a person is infectious, or that the disease will make a comeback.Some survivors say symptoms can linger for months. Catherine Hayes, who works at the water and sanitation department in Vail, Colo., says she hasn't fully regained her sense of taste and smell a month-and-a-half after her symptoms surfaced in late March. "It's strange," says Ms. Hayes, particularly because she reports having a mild case of the illness.– Write to Preetika Rana at preetika.rana@wsj.com

Scientists investigate why some test positive for Covid-19 twice – The Wall Street Journal

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