SCIENTISTS in Hong Kong have confirmed the world’s first case of coronavirus re-infection, suggesting herd immunity will not work and sparking fears the virus may never disappear.

Researchers at University of Hong Kong’s (HKU) Li Ka Shing Faculty of Medicine used genome sequencing to show that the patient had been infected by two “clearly different” virus strains.

The sequencing proved that the virus had infected the man on two separate occasions and it was not a case of “viral shedding”, when a virus releases progeny after a successful reproduction during a host-cell infection.

The patient is an “apparently young and healthy” 33-year-old man residing in Hong Kong.

He was returning to the Asian city from Spain, traveling via the UK, when he was found to be positive for the coronavirus on August 15, 2020.

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The man had previously tested positive for the virus on March 26, 2020, and was hospitalised with the disease three days later.

He was discharged from hospital on April 14 following two negative tests for Covid-19 taken 24 hours apart.

Researchers reported that the patient remained asymptomatic throughout his second infection, which occurred 142 days after the first.

This suggests that subsequent infections may be milder than the first, but the researchers were hesitant to draw concrete conclusions.

They said: “This is the world’s first documentation of a patient who recovered from Covid-19 but got another episode of Covid-19 afterwards.

“Before this report, many believed that recovered Covid-19 patients have immunity against re-infection.

“However, there is evidence that some patients have waning antibody levels after a few months.”

The published report goes on: “This case illustrates that re-infection can occur after just a few months of recovery from the first infection.

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“Our findings suggest that SARS-CoV-2 may persist in the global human population as is the case for other common-cold associated coronaviruses, even if patients have acquired immunity via natural infection.”

The scientists add that, as immunity may be short-lasting, any vaccine should be administered to everyone, including those who have already been infected.

As a result, they say herd immunity is “unlikely” to be able to eliminate Covid-19, and it will probably “continue to circulate” through the population as “seasonal” coronaviruses do.

Furthermore, they recommend that even those who have recovered from Covid-19, and so are assumed to be unable to transmit the virus, should “comply with epidemiological control measures such as universal masking and social distancing”.

Responding to the study on Twitter, Yale School of Medicine's Professor Akiko Iwasaki wrote: "Kudos to the scientists for this study. This is no cause for alarm - this is a textbook example of how immunity should work.

"Second infection was asymptomatic. While immunity was not enough to block re-infection, it protected the person from disease.

"Patient had no detectable antibody at the time of re-infection but developed detectable antibody after re-infection. This is encouraging.

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"Since re-infection can occur, herd immunity by natural infection is unlikely to eliminate #SARSCoV2. The only safe and effective way to achieve herd immunity is through vaccination.

"Lastly, while this is a good example of how primary infection can prevent disease from subsequent infection, more studies are needed to understand the range of outcomes from reinfection."

The research was led by Dr Kelvin Kai-Wang To, Professor Ivan Fan-Ngai Hung, and Professor Kwok-Yung Yuen.

Their study was accepted by the international medical journal Clinical Infectious Diseases today (August 24, 2020).