Researchers in Hong Kong have reported what they said was the first confirmed case of COVID-19 reinfection in August, after the person recovered from an earlier infection by SARS-CoV-2 in late March. The 33-year-old man was reportedly infected a second time during travel in Europe.

The evidence documented for COVID-19 reinfection has raised questions around how durable our immunity really is against SARS-CoV-2 – either naturally or with a vaccine. The big issue with our current understanding of the reinfection puzzle is decoding the many kinds of immune responses the human body has to the virus, experts have said, 

In the Hong Kong case, the man had travelled to Spain and returned to Hong Kong via the United Kingdom. A saliva sample was taken upon arrival in Hong Kong as part of a screening protocol and tested positive for SARS-CoV-2 on Aug. 15.

Researchers at the University of Hong Kong sequenced the virus from the first and second bouts of infection. This analysis showed that the two sequences did not match, suggesting that the second bout of COVID-19 was not linked to the first. There was a total of 24 differences in the sequences of the two infections.

There were also no antibodies found in a blood sample taken soon after a positive test at the airport before his travel. This is a key indication that the second virus had not been lingering unnoticed for months, and strong evidence of reinfection.

“This is certainly stronger evidence of reinfection than some of the previous reports because it uses the genome sequence of the virus to separate the two infections,” Jeffrey Barret, a senior scientific consultant for the COVID-19 Genome Project at the Welcome Sanger Institute, commenting on the study to AFP.

Even so, reinfection is rare

The researchers highlight the need for caution against reinfection, even if very rare.

“Our study proves that immunity for COVID infection is not lifelong – in fact, reinfection can occur quite quickly,” Kelvin Kai-Wang To, lead author of the forthcoming study, and microbiologist at Hong Kong University’s Faculty of Medicine, told AFP.  “COVID-19 patients should not assume after they recover that they won’t get infected again.”

Experts not linked with the study concur, adding that the finding doesn’t change the need for a working vaccine against SARS-CoV-2.

“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,” Brendan Wren, professor of microbial pathogenesis at the London School of Hygiene & Tropical Medicine, told Financial Times.

In contrast, other experts are reassured to some extent by the case, since the second infection was asymptomatic — suggesting that the immune system might have played a part in reducing the severity of the disease, even if it did not neutralize the virus in his body.

“It is very hard to make any strong inference from a single observation,” Jeffrey Barrett from the Wellcome Sanger Institute COVID-19 Genome Project. “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.”

In a 13 April study from South Korea, 116 recovered cases of COVID-19 were found positive again. The study poured over these reported cases of reinfection, and concluded that the virus detected in all the recovered patients was simply leftover dead virus from the earlier infection flaring up as false positives.

Considering the evidence on both sides, it isn’t surprising that the news about ‘proof’ from Hong Kong is met with caution by most experts, since the study offers limited evidence towards the overarching concerns around reinfection.

Many parts of India are still under varying degrees of lockdown and control. AP

Reinfection is a key consideration for vaccines

The intensity and duration of the body’s immune response to the SARS-CoV-2 virus has been questioned time and again. It is a crucial determining factor in how long vaccines will be effective for, and how frequently a booster dose is needed.

Antibodies are agents of the immune system that are produced rapidly in the body’s fight against an infection, or a threat to the immune system is discovered. The number of these initial antibodies is known to decline between the first to third month of recovery, depending on how severe the infection was. But for COVID-19, whether the antibody decline makes us more vulnerable to reinfection is a still a mystery.

Being able to tell the difference between a reinfection with COVID-19 and a relapse of the same infection will help medical teams tighten treatment procedures for patients. It will also bring experts a step closer to understanding and eliminating the novel coronavirus.

To the public, proof that reinfection is possible will also bring clarity on the testing process, its potential inaccuracies, and limit alarmism and any false information or speculation that might be making the rounds about COVID-19 reinfection.

Experts around the world are cautiously stressing that reinfection is rare (if not very rare).

However, considering the many unknowns about the SARS-CoV-2 virus, it might still be risky to tout this theory as a fact. This, because declaring reinfection is not possible, may give people a false sense of security, which could be potentially dangerous.