Confirmed cases of COVID-19 reinfection in Hong Kong, EU, India don't change vaccine agenda, experts say
The intensity and duration of the immune response against SARS-CoV-2 is a crucial in determining how long vaccines will be effective for, and how frequently a booster is needed.
Researchers in Hong Kong have reported what they say is the first confirmed case of COVID-19 reinfection. The patient supposedly fell ill with COVID-19 in August, after having recovered from an earlier infection by SARS-CoV-2 in March 2020.
The 33-year-old man from Hong Kong was reportedly infected a second time during a stint of travel in Europe. He 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 15 August.
Two patients in Europe have also been confirmed to have been re-infected with COVID-19 . The evidence gathered for COVID-19 reinfection has raised questions around how durable our immunity really is against SARS-CoV-2 – either naturally or with a vaccine. People’s immunity to the coronavirus , and how best to tame the pandemic are still areas being explored, experts have said.
The Health Minister of Telangana announced the day after the Hong Kong case made news, that at least two cases of coronavirus reinfection have taken place in the state.
'No antibodies', strong evidence
Researchers sequenced the virus from the 33-year-old Hong Kong man's first and second bouts of infection. This comparison showed that the two sequences did not match – there was a total of 24 differences in the sequences of the SARS-CoV-2 virus from both infections. In other words, the second bout of COVID-19 was not linked to the first.
In addition, there were no antibodies found in a blood sample taken from him soon after his positive test at the airport during 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 Indian Council of Medical Research (ICMR) Director-General Balram Bhargava said at a press briefing that the Hong Kong case is likely a rare exception, and that reinfection depends on multiple different factors.
"We have read with interest the reports of reinfection in one case in Hong Kong. We are learning more and more about the disease as we go ahead. It can depend on several factors, one can be related to the patient itself, how is his immunity, how was his immune status, was it compromised. It can also depend upon the virus, whether the virus has mutated or turned virulent," he said, as per a Livemint report.
Even if rare, the Hong Kong researchers highlight the need to be cautious and aware of the reinfection risk.
"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 – that the finding doesn't change the need for precautions and working vaccines 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.
Other experts are reassured to some extent by the Hong Kong 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.
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.
Hong Kong authorities have taken a tougher stance on opposition following Beijing’s imposition of a national security law on the city, arresting prominent pro-democracy activists and participants in anti-government protests in 2019.
The killer T cell responses remained largely intact, as per the study, and could recognize virtually all mutations in the variants.
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