A healthcare worker conducts a swab test for Covid-19 in Brussels on July 27, 2020.
AMSTERDAM/HONG KONG (REUTERS, BLOOMBERG) – A patient in the Netherlands and another in Belgium have been confirmed as having been reinfected with the coronavirus, Dutch national broadcaster Nos reported on Tuesday (Aug 25), citing virologists.
The news follows a report this week by researchers in Hong Kong about a man there who had been reinfected four and a half months after being declared recovered.
The Nos cited virologist Marion Koopmans as saying the Dutch patient was an older person with a weakened immune system.
She said that cases where people have been sick with the virus a long time and it then flares up are better known.
But a true reinfection, as in the Dutch, Belgian and Hong Kong cases, requires genetic testing of the virus in both the first and second infection to see whether the two instances of the virus differ slightly.
Dr Koopmans, an adviser to the Dutch government, said reinfections had been expected.
“That someone would pop up with a reinfection, it doesn’t make me nervous,” she said. “We have to see whether it happens often.”
The Belgian patient had mild symptoms, the Nos cited virologist Marc Van Ranst as saying.
But “it’s not good news”, he added.
He said the case shows antibodies the patient developed during the first exposure were not enough to prevent a second case with the slightly different variant of the virus.
He said it is not clear whether such cases are rare or whether there are “many more people who could have a reinfection after six or seven months”.
In Hong Kong, the 33-year-old man’s second Sars-CoV-2 infection was detected via airport screening on his return to Hong Kong from Europe this month.
Researchers at the University of Hong Kong used genomic sequence analysis to prove that he was infected by two different strains.
The information technology worker did not develop any symptoms from his second infection, which might indicate “subsequent infections may be milder”, the researchers said.
“Our findings suggest that Sars-CoV-2 may persist in humans,” Dr Yuen Kwok-Yung and his colleagues said on Monday in a paper accepted for publication in the journal Clinical Infectious Diseases.
The findings also suggest that Sars-CoV-2 is reminiscent of the coronaviruses that cause the common cold, and may continue to circulate “even if patients have acquired immunity via natural infection or via vaccination”, they said.
While some patients have tested positive for the virus over many weeks, even after their symptoms have resolved, scientists have not fully understood whether these cases reflect lingering traces of the virus, a re-eruption of an infection, or a new infection.
It may be difficult to find Covid-19 survivors who have been reinfected with Sars-CoV-2 if they do not show symptoms, said Dr Corey Smith, head of translational and human immunology at the QIMR Berghofer Medical Research Institute in Brisbane.
“Because he showed no symptoms on the second infection, it is likely that, although the virus has managed to establish infection, his memory immune response has likely prevented any symptomatic disease,” Dr Smith said in an e-mail.
“This does suggest that natural infection may provide protection against disease, but not reinfection.”
One problem is that a reinfected person may still spread the Sars-CoV-2 virus to someone who has not been previously exposed, he said.
It is inevitable that reinfections will occur, said Dr Thomas File, president of the Infectious Diseases Society of America and chairman of infectious diseases at Summa Health, a hospital system in Akron, Ohio.
“The question is how long after the initial infection might that occur?” he said.
Protection from reinfection will vary between people, and may depend on the individual patient, their immune system, whether the patient developed symptoms to the first infection, and the nature of the second virus to which they have been exposed, Dr File said in an interview on Monday.
“We know that if you look at the seasonal endemic coronaviruses, the amount of immunity can be as low as four, five or six months to maybe up to a year or two,” he said.
Worldwide, some 24 million people are known to have been infected with Covid-19, Dr Maria Van Kerkhove, the World Health Organisation’s technical lead on Covid-19, told reporters in Geneva on Monday. Most patients – even those who have a mild case – mount an immune response to the infection, she said.
It is important to document cases like the one described in Hong Kong, “but not jump to any conclusions”, Dr Van Kerkhove said.
Studies tracking larger numbers of cases over time are needed to better understand the quality and durability of recovered patients’ neutralising antibody response to Sars-CoV-2, she said.
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