Take-away lunch Hong Kong restaurant coronavirus
A worker holds a plastic bag containing a take-away lunch at a restaurant, following the coronavirus disease (COVID-19) outbreak in Hong Kong, China, July 29, 2020. Scientists in Hong Kong have shown genetic evidence confirming viral reinfection with SARS-CoV-2. Image Credit: Reuters


  • Scientists have shown first genetic evidence confirming viral reinfection with SARS-CoV-2.
  • The research team found that a man in Hong Kong was reinfected (tested COVID-19 positive again) four months after the first infection — after returning from Spain via the UK.
  • It's the first time scientists demonstrated reinfection, using comparative genetic analysis.
  • The man was re-infected with another variant of the SARS-CoV-2.
  • The first infection was mild (in March 2020), while the second (July 2020) was "asymptomatic".

DUBAI: For the first time, scientists have shown genetic evidence confirming viral reinfection with SARS-CoV-2.

Reinfection means getting infected by the same virus (albeit a different strain) again, after full recovery— and testing negative — from the first infection.

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How did it happen? Researchers at the University of Hong Kong (UHK) followed the case of a 33-year-old man in Hong Kong who fell ill with COVID-19 in March and recovered in April.

Four months after the first infection (in July), he tested COVID-19 positive again — after returning from Spain via the UK, according to Nature.

“Our results prove that his second infection is caused by a new virus that he acquired recently, rather than prolonged viral shedding,” said Dr Kelvin Kai-Wang To, a clinical microbiologist at the UHK.

“Our findings suggest that SARS-CoV-2 may persist in humans as is the case for other common-cold associated human coronaviruses, even if patients have acquired immunity via natural infection or via vaccination,” the authors said in a press statement. “Further studies on reinfection, which will be vital for the research and development of more effective vaccines, are warranted.” 

They cited the case as clear evidence of reinfection of the SARS-CoV-2, the virus that causes the coronavirus diease (COVID-19).

Typically, people who were infected with the coronavirus mount an immune response. That immune response is thought to prevent most reinfections from the same strain.

How was the reinfection confirmed?

Researchers used comparative genetic analysis. The Hong Kong team genetically sequenced the virus from both rounds of infection.

They said the man was re-infected with COVID-19, but with another variant of the SARS-CoV-2.

Does that mean the virus has mutated?

Yes. Typically, people who were infected with the coronavirus mount an immune response. That immune response is thought to prevent most reinfections from the same strain.

However, scientists said the durability of that protection from subsequent SARS-CoV-2 infection remains unclear.

How long does immunity from coronavirus last? Does that mean immunity can wane?

Previous studies show that the SARS-CoV-1 virus triggered memory cells against the virus that were still present 17 years later.

That study, conducted by a Singaporean team, shows the longest presence of immunity markers for any coronavirus family.

As for SARS-CoV-2 immunity, there’s no scientific evidence of long-term immunity available. The reported reinfection case indicates that immunity can wane, researchers said.

Viral shedding 16
*VIRAL SHEDDING = the expulsion/release of virus progeny (offspring) following successful reproduction during a host-cell infection. Image Credit: Gulf News / Jay Hilotin Source: https://bit.ly/2Up12b3

What's the difference between the first infection and the second one?

Comparing two genetic sequences, the authors found that there was a 24-nucleotide difference between the viruses from the first and second episodes. This resulted in amino acid changes in nine proteins.

Genetic analyses showed that the first viral genome was closely related to earlier strains present in the US or England, while the second was closely related to strains collected from Europe in July and August.

What’s the difference between reinfection and prolonged viral shedding?

The journal Nature clarified in an article the difference between reinfection and prolonged viral “shedding”.

Previously-reported reinfections have been found to relate to prolonged shedding (transmissibility) of the virus or its genetic material, instead of being real cases of reinfections. There were no comparative genetic sequencing done on samples taken from the same patients to back the reinfection claim.

Recovered people are known to shed viral fragments for weeks, which can cause tests to show a positive result (using an antibody test), though there’s an absence of live virus (confirmed using PCR test).

Did the reinfected man die?

No, he didn’t die. He was reported asymptomatic following the second infection.

The man had only mild symptoms in the first infection, and absolutely no symptoms in the second one.

Given the asymptomatic from the second infection, indicates that the man’s immune system responded by producing a fresh batch of antibodies, Nature reported.

Is this the first case of reinfection ever?


Common cold coronavirus strains (including types 229E, NL63, OC43, and HKU1, usually cause mild to moderate upper-respiratory tract illnesses) are known to cause reinfections in less than a year.

Had there been COVID-19 reinfection cases in the US and other countries?

It's not clear. There had been only presumed reinfections in the US and elsewhere. But none of those cases have been confirmed with genetic tests.

Experts had hoped that the new coronavirus might behave more like its cousins SARS and Middle East respiratory syndrome (MERS), which seemed to produce longer-lasting immunity of a few years.

What are the implications of this reinfection case for vaccines?

It suggests that immunity to the coronavirus may last only a few months, in some people. Experts also said that it has implications for vaccines being developed for the virus. Those implications are unclear at this point.

It’s also unclear how the immunity that may be conferred by any approved coronavirus vaccine would last.

However, given that there are millions of cases worldwide, it’s expected that a few, or even a few dozen, people might be reinfected with the virus after only a few months.

Due to the possibility of reinfection, the authors suggested that recovered COVID-19 patients should also be considered for vaccine, when they shots become available.

The authors also recommended that individuals infected with COVID-19 in the past should continue to comply with precautionary measures -- wearing face masks and practicing social distancing. 

What are were genetic strains seen?

In the second bout of coronavirus infection, the genetic sequence of the virus found in him closely matched the strain circulating in Europe in July and August, the report said.

D614 strain of the SARS-CoV-2 was dominant initially.G614 (known to scientists as just the “G” strain) eventually took over.
Image Credit: Gulf News / Cell

The new SARS-CoV-2 variant carrying the change (mutation) in the spike (S) protein is known as the G614 mutation.

What’s the G614 strain?

A team of virologists found that the new “G614” SARS-CoV-2 strain has become the most prevalent strain in the global pandemic. The new strain is named after the genetic instructions for one of the amino acids — number 614 — seen to have switched from a “D” (short for aspartic acid) variant to a “G” (short for glycine).

How many mutations have been seen in the SARS-CoV-2 spike?

A US-British research team identified at least 14 mutations in the spike protein, but highlighted that the mutation spike G614 is of "urgent concern”.

It’s also been reported that the new strain makes the virus more infectious, but less deadly.

Is it a good thing?

Evolutionary biologists say that a virus strain that kills a host instantly fizzles out eventually — but would then be unable to spread its genetic information to another host.

Scientists all over the world are collecting samples from patients with COVID-19, sequencing the virus’ genetic code, and uploading the data to a scientific server, called GISAID. Data collected so far show that SARS-CoV-2 mutates an average of 2 mutations per month.

What they found, as the virus travels within and between countries, it mutates — a reaction to evolutionary pressure from the population it infects.

The authors of the Hong Kong study stated: “Further studies on reinfection, which will be vital for the research and development of more effective vaccines, are warranted.”

Emerging data suggest that while the new dominant coronavirus strain is more infectious, enabling it to spread far and wide, it has also become less lethal.