Mystery infection that could derail vaccine
A mystery man or woman in Victoria who tested positive for COVID-19 twice is now the subject of intense interest among virus researchers around Australia.
Victorian Premier Dan Andrews' confirmation that medical experts are treating the case as the nation's first ever reinfection will likely spark international attention.
Reports of reinfection with SARS-CoV-2 are rare internationally but have previously emerged in Hong Kong, the Netherlands and Belgium, and Ecuador.
But as debate rages over how or even if this is possible here in Australia, scientists are certain of one thing.
The length of time between the first and second positive test in this Victorian case has raised alarm bells among COVID-19 experts.
VICTORIAN CASE 'EXTREME' AND 'RARE'
Melbourne University epidemiologist and public health specialist Tony Blakely told news.com.au that the fact the person had first contracted COVID-19 in July and had then tested positive again in late October was a "rare and an unusually long time frame" for someone simply shedding the original virus.
"There are two biological possibilities. It is not impossible that someone could be shedding weeks later," he said.
"Some months later? That seems quite extreme. So, the second possibility is they have genuinely been reinfected."
In other words, both possibilities are "extreme" and "rare."
"So the two possibilities are one, a biological extreme that they are still shedding the virus. The second possibility is also a biological extreme, which is someone getting reinfected," he said.
IMPLICATIONS FOR COVID-19 VACCINE
The risk of reinfection also has implications for countries that have pursued controversial herd immunity strategies and the development of a safe vaccine.
If you can be reinfected it raises questions over how frequently Australians will need to be vaccinated.
"On the vaccine side, everyone will be looking at this worried about what it means for the effectiveness of a vaccine," Prof Blakely said.
"But you can't read much into only one case."
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When the vaccine is first rolled out, Prof Blakely said it was expected to be "imperfect" and may not provide immunity to all.
"Maybe 70 per cent. We are all guessing. Who knows. We don't know how much is going to be immediately failing for the vaccine - they simply don't develop immunity,'' he said.
MYSTERY OVER WHY CASE WAS RE-TESTED
Australian molecular immunologist and viral immunologist Gabrielle Belz also told news.com.au that the mysterious case was unusual because of the length of time between the first and second test.
It was also not clear whether the person was sick again or simply retested without symptoms.
"Given the first infection/testing was in July it would seem like a very long shedding period (of viral remnants rather than active virus) and I was curious as to why the gentleman was retested," she said.
"I assumed he was showing some symptoms that led to retesting but we have been provided the information on the full circumstances around this individual and thus it can't be assumed; the expert panel would be considering the fuller information."
It's not known if the Victorian case tested negative for COVID-19 in the intervening period.
GENOMIC TESTING COULD SOLVE MYSTERY
Overseas, genomic testing has proved crucial to determine whether people who have tested positive twice have been reinfected or are simply shedding old viruses.
"It doesn't seem to have been confirmed definitively either way as yet, and I would think that ongoing analyses sequence the 2 viruses to determine if they were different, or the same," Prof Belz said.
"In general, viruses do not infect a second time like this but can in rare circumstances regardless of the virus. The immune system does a very good job of defending the body against a second infection to largely prevent this from happening. It is a very efficient system that arms the body against viral and bacterial invaders.
"If and when the full picture is known, it is a reinfection, it will be very interesting to study this individual."
FIRST RE-INFECTION REPORTED IN HONG KONG
Scientists only reported what was believed to be the first confirmed case of reinfection - a 33-year-old man from Hong Kong - in August.
According to the British Medical Journal, researchers from the University of Hong Kong's Li Ka Shing Faculty of Medicine Department of Microbiology "found that the patient's two episodes were caused by virus strains with clearly different genome sequences."
"The man first acquired this infection in March, locally, probably from a colleague who travelled from London to work with him. At that time he had very mild symptoms and tested positive for COVID-19," said Ivan Fan-Ngai Hung, research team member and clinical professor in the university's Department of Medicine.
"When he was hospitalised three or four days later he was already asymptomatic - all confirmed positive cases of COVID-19 in Hong Kong are hospitalised for observation, symptomatic treatment, and prevention of onward transmission - and remained in hospital for three weeks until he tested negative twice.
"After that, he was very well until four and a half months later, when he came back to Hong Kong having been in Spain for a week, and he was tested on return, because everyone gets tested on arrival in Hong Kong. He was asymptomatic but still tested positive and had quite a high viral load."
After the Hong Kong case emerged, the scientific journal Nature reported in September at least one immunologist found the news strangely reassuring as it was a "nice textbook example of how the immune response should work".
However, when US authorities reported another likely reinfection in Nevada with more severe symptoms it raised alarm bells.
In October, the Lancet reported the case of a 25-year-old man in the US state of Nevada who presented to health authorities on two occasions with symptoms of viral infection.
The patient had two positive tests, the first on April 18, 2020, and the second on June 5, 2020, separated by two negative tests done during follow-up in May, 2020.
It's not known if the Victorian individual had a negative test in the intervening period.
Genomic analysis of SARS-CoV-2 showed genetically significant differences between each variant associated with each instance of infection in the Nevada case.
The Hong Kong case also raised the prospect that reinfection could occur when people are exposed to new strains of the virus.
The Hong Kong man's second infection, for example, occurred after he had travelled overseas to Spain.
That's clearly not a possibility in the Victorian case where the international airport remains closed.
EXPERT PANEL TO REVIEW VICTORIAN CASE
Premier Andrews said the case had been reviewed by an expert review panel to determine whether it was ongoing viral shedding or a new case.
"And I can confirm that they have reviewed this particular case and concluded there wasn't enough evidence to say that the positive test presented viral shedding, so the case is being monitored closely,'' he said.
"Through an abundance of caution … we are assuming that is a positive case, rather than the person shedding after the original infection.
"This is understandably frustrating for everyone involved, whether this is in fact a positive case or not, but we do take a very cautious approach, and I think that is the best way to go. In fact the only way.
"If that is the case, it's better to be cautious. If that is the case then that will be one of only a handful of those sorts of reinfection cases we have seen anywhere in the world."
Asked if the infected person was a hospital worker, the Victorian Premier declined to reveal those details.
"I have no details on who they are but again if it's appropriate to speculate or confirm that in any way, I'm more than happy to make sure there is an update,'' he said.
Originally published as Mystery infection that could derail vaccine