SINGAPORE – The news that a 33-year-old man in Hong Kong has been reinfected with Covid-19 has raised fears that others may get the disease more than once, but infectious disease experts have said it is rare and is not a cause of fear unless more cases arise.
Most people develop a physically powerful immune reaction after infection with Covid-19, but for recently unknown reasons, the Hong Kong type was unable to identify an antibody reaction to the first infection last March.
He was hospitalized and discharged on April 14 after two negative samples of nasopharynge and throat. He was then positively tested positive for Covid-19 on 15 August, after returning from a holiday to Spain via Britain.
Researchers from the University of Hong Kong (HKU) said they discovered the world’s first documented case of reinfection after sequencing the virus from human infections and discovering that it had a different strain than it was in March.
Professor Paul Tambyah, lead representative in infectious diseases at National University Hospital, said: “The most likely explanation for why it was reinfected with another strain is that it had no detectable antibodies after the first infection, perhaps because it was very benign (it was asymptomatic for its hospitalization) but also perhaps because of an express immune defect.”
This turns out to be a rare case, “just like we have other people who have two episodes of chickenpox or even measles,” he added.
Worldwide, there are more than 23 million cases, and before the Hong Kong case, there were only a few anecdotal reports of other people reinfected with Covid-19.
Interestingly, the Hong Kong boy showed no symptoms at the time, whereas when he first had an infection, the symptoms were mild.
Professor Tambyah said the first infection appears to have protected humans from a serious infection at the time of exposure. This also prepared him for an expired antibody reaction when he was exposed to the virus again, even though it was another strain.
On Twitter, Professor Akiko Iwasaki, an immunologist at Yale University, said human immunity had him from the disease, even if it wasn’t enough to block reinfection.
He said it is encouraging to note that if the patient did not have detectable antibodies at the time of reinfection, he developed detectable antibodies after reinfection.
He also stated that, since reinfection may occur, collective immunity through herbal infection is unlikely to eliminate the virus that causes Covid-19. The only effective way to discharge collective immunity is vaccination.
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HKU researchers reportedly stated that the case of reinfection would mean that those inflamed with Covid-19 would still receive the vaccine and comply with mask tests and social distance restrictions.
It is expected to be published in the US journal Clinical Infectious Diseases.
“This is an exclusive case, however, represents anything we discover credible: that post-infection immunity would possibly not last a lifetime, like other human coronaviruses or influenza,” said Associate Professor Hsu Li Yang, NUS’ Saw School of Public Health Swee Hock.
Vaccine immunity would possibly not be for life either, but it would possibly be more like the flu vaccine, where repeated vaccines are needed, he added.
However, Professor Ooi Eng Eong, deputy director of the Emerging Infectious Diseases Program at Duke-NUS School of Medicine, noted that the immune reaction to vaccination is different from that opposed to Sars-CoV-2 infection.
“The genetic elements of the virus are able to suppress our immune response, while vaccines are designed to stimulate responses,” he said.
“The immunity resulting from vaccination and infection would be different.”
There are still some unknowns about the Hong Kong case. For example, it is not known whether the reinfected type was able to mount a T-cell reaction to the initial infection, even though it did not have an antibody reaction, Professor Tambyah said.
He added that knowing this would lead to a greater understanding of the point of immunity that a vaccine must reach to not only save a serious illness, but also save an asymptomatic infection.
T cells are a component of the immune formula that also helps us fight disease.
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In July, an examination through Professor Antonio Bertoletti in the Duke-NUS Emerging Infectious Diseases Program and his team reported that T cells would likely offer lasting immunity against Covid-19.
The results, published in the journal Nature, showed that patients who recovered from Sars 17 years ago, after the 2003 outbreak, still had reminiscent T cells, which identified portions of Sars-Cov-2, the virus that causes Covid-19.
The team also evaluated others who were not inflamed with Covid-19 and discovered specific sars-Cov-2 T cells in more than a portion of them, suggesting that a pre-existing Sars-Cov-2 immunity point is provided in the general population.
In a recent Facebook post reproduced on the HKU website, assistant clinical professor Siddharth Sridhar from HKU’s Department of Microbiology stated that for the maximum number of people, an infection with Covid-19 would confer a physically powerful immune reaction. This reaction is probably the most likely contrary to severe symptomatic reinfection, at least in the short term.
“Some patients with asymptomatic or inflamed Covid-19 have low antibody reactions that are minimized quickly, but still expand a strong ‘T lymphocyte’ reaction,” he said.
“Our immune formula will adapt to this virus and treat it (hopefully with the help of vaccines),” he said.
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This article was first published in The Straits Times.