Hong Kong case leads scientists to doubt development of antibodies in previous patients due to reinfection case, but other experts say it is no cause for alarm

A young man has been diagnosed with coronavirus more than four months after he recovered from a first episode of the disease, suggesting that immunity to the virus can be short-lived and raising more questions about vaccines against Covid-19.

The case in Hong Kong is the first lab-confirmed reinfection. Genetic sequencing by scientists at the University of Hong Kong established that the second episode, in an otherwise healthy young man, was caused by a slightly different strain. Researchers had hoped that the man’s immune system would still have recognised and fought off the virus at the second encounter.

Dr Kelvin Kai-Wang To and colleagues say people who have recovered from Covid-19 should not be assumed to be immune. They should still be offered vaccination, once it is available, and should also comply with mask-wearing and social distancing restrictions.

“Our findings suggest that Covid-19 may persist in the global human population, as is the case for other common-cold associated human coronaviruses, even if patients have acquired immunity via natural infection,” they said in a statement.

The 33-year-old man was unaware that he had caught the virus a second time. He was returning to Hong Kong from Spain on a flight via the United Kingdom. His infection was detected when he was tested on entry at Hong Kong airport on 15 August and was taken to hospital, where he remained until he was clear of the virus – although at no point did he show symptoms.

His first infection was in March, when he suffered from a fever, cough, sore throat and headache for three days, but recovered quickly.

The researchers say they are certain this is a case of reinfection and not of the virus lingering in the body, not least because the first genetic sequence belonged to a different clade, or lineage, than the second. There have been rare reports of “viral shedding”, where the infection lingers – notably in a pregnant woman in whom the virus was detected 104 days after her previous positive test.

The sequencing also showed that the man’s virus was similar to the strain circulating in Europe, where Covid-19 is resurgent, according to the report, which has been accepted for publication in the American journal Clinical Infectious Diseases.

But other scientists suggested there was little cause for alarm. Dr Jeffrey Barrett, a consultant to the Covid-19 Genome Project at the Wellcome Sanger Institute, said the Hong Kong researchers might have come to overly sweeping conclusions.

“Given the number of global infections to date, seeing one case of reinfection is not that surprising, even if it is a very rare occurrence. I think their ‘implications’ are far too broad given that they have seen just one instance. This may be very rare, and it may be that second infections, when they do occur, are not serious – though we don’t know whether this person was infectious during their second episode,” he said.

Brendan Wren, professor of microbial pathogenesis at the London School of Hygiene and Tropical Medicine, said: “With over 3m cases of Covid-19 worldwide, the first reported case of a potential re-infection with Covid-19 needs to be taken into context. It appears that the young and healthy adult has been reinfected with a slight Covid-19 variant from the initial infection three months previously.

“It is to be expected that the virus will naturally mutate over time. This is a very rare example of reinfection, and it should not negate the global drive to develop Covid-19 vaccines.”

The article is originally published at "The Guardian"