Researchers at the University of Hong Kong said a man who recovered from Covid-19 was infected again four-and-a-half months later in the first documented instance of human re-infection, Reuters reported. The 33-year-old IT worker was discharged from a hospital in April. He tested positive for the virus again after returning from Spain earlier this month.
The health officials were unsure at first if the Hong Kong man was a “persistent carrier” of the virus from his previous infection. But the researchers at the University of Hong Kong have confirmed that the virus strains contracted by the IT worker in April and August were “clearly different”. Their study has also been accepted by the Clinical Infectious Diseases journal.
“Many believe that recovered Covid-19 patients have immunity against re-infection because most developed a serum neutralising antibody response. However, there is evidence that some patients have waning antibody level after a few months,” the researchers were quoted as saying by RTHK news.
The researchers also said that the patients who have recovered from Covid-19 should also wear masks and maintain social distancing. Their findings suggest that the SARS-CoV-2 may persist in the global human population just like other common cold-associated human coronaviruses, even if patients have acquired immunity through natural infection.
After contracting coronavirus, the immunity can be short-lasting so vaccination should also be considered for them, the researchers noted in their findings.
“The finding does not mean taking vaccines will be useless,” Dr Kai-Wang To, one of the leading authors of the paper, told Reuters. “Immunity induced by vaccination can be different from those induced by natural infection. We will need to wait for the results of the vaccine trials to see if how effective vaccines are,” he said.
There have been a few instances of people around the world who have been declared recovered, testing positive again, raising fears of re-infection. A new guidance from the Centers of Disease Control and Prevention (CDC) in the United States recently 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. 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.
“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.
The novel coronavirus has infected over 23.31 million people across the globe and 805,075 people have succumbed to the virus, according to a Reuters tally.
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