Is it possible to catch COVID-19 twice? Hong Kong reports first documented case of re-infection

A Hong Kong man, who had first tested positive for COVID-19 in March and made a full recovery, was re-infected months later after making a trip overseas, according to researchers.

A pre-print study by a team at the University of Hong Kong purports to be the "world's first documentation" of a patient who recovered from coronavirus, contracting the infection again.

Researchers sequenced the genome of his first and second infections to show that virus strains were different, suggesting that he was re-infected.

Although there have been unconfirmed reports of people contracting COVID-19 again after recovering from the virus, the study, which has not been peer-reviewed, has potential implications for vaccine use and policies pertaining to the concept of herd immunity which presumes that those who recover from the disease will not be re-infected.

Hong Kong man gets re-infected despite being asymptomatic

The Hong Kong man, a 33-year-old IT worker with a history of good health, had first tested positive for COVID-19 in late March. He had symptoms of fever and cough and was rushed to the hospital.

The patient recovered and was discharged in mid-April after testing negative for the infection. However, in August, after visiting Spain via the UK, he again tested positive when he returned to Hong Kong, despite being asymptomatic.

In the research paper, study author Kwok-Yung Yuen and his colleagues suggested that herd immunity is unlikely to eliminate coronavirus and a potential vaccine might not provide lifelong immunity to the infection.

However, some immunologists asserted that the case was not a surprise and suggested a more positive interpretation of the findings. "This is a textbook example of how immunity should work," Akiko Iwasaki, an immunology expert at Yale University, said in a tweet on Monday, while referring to the Hong Kong man's asymptomatic case.

Iwasaki said the research had "no bearing" on the success of a potential COVID-19 vaccine. "Vaccines can provoke a much higher level of immunity in a person that can potentially block re-infection, or at least shut it down to a noncontagious level," she added.

The study was accepted in the Clinical Infectious Diseases journal on Monday and it is likely to be published online the next day, according to Lili Kadets, a journal spokeswoman.

It was 'reviewed and accepted' by Robert T Schooley, an infectious-diseases expert at the University of California at San Diego.

Here's what re-infection might mean

The Hong Kong man's re-infection may suggest the level of immunity after contracting infection may be lower than many had hoped, or can reduce overtime, or may occur on a spectrum, thereby offering partial immune protection, according to The Washington Post.

The paper suggested that while the man had no detectable antibodies after contracting the infection for the second time, he developed them afterward -- a development Iwasaki termed as "encouraging".

"What we are learning from this new case report is that SARS-CoV-2 may persist in the global population, similar to other common cold-associated human coronaviruses, even if patients have some degree of acquired immunity," Robert Glatter, an emergency physician at Lenox Hill Hospital in New York City said in an interview.

"The only safe and practical approach to achieve herd immunity is through vaccination," he said, although immunisations may not provide lifelong protection.

Glatter added that extensive studies are needed to "evaluate the spectrum of illness and degree of immunity achieved due to the re-infection by the virus."

"The take-home is that a vaccine, no matter how novel or sophisticated, may not be able to provide lifelong immunity against COVID-19. This is in keeping with other seasonal coronaviruses," he was quoted as saying.

He said it may be possible that vaccines should be administered twice a year to supplement natural immunity, The Washington Post reported.

Authors of the University of Hong Kong study have recommended that patients who recover from COVID-19 should continue to follow social distancing and other norms, such as wearing a mask.