While most people by now are aware of the symptoms of coronavirus, it is possible for someone to be infected by the disease and not display any signs of illness.
It was previously speculated nearly half of all patients diagnosed with COVID-19 don’t experience any symptoms.
Speaking to Yahoo News Australia in a livestream Q&A last week, virologist Professor Ian Mackay from the University of Queensland acknowledged the concern around COVID-19 patients without symptoms, but pointed out asymptomatic spread is just like any virus.
“The same sort of thing happens with influenza,” he said.
“We’re really hyper-focused on what it [COVID-19] might do, and the reality is we already knew these sorts of events could happen.
“With this virus we know asymptomatic spread is possibly a major factor.”
In a follow-up interview with Yahoo News Australia, Prof Mackay said an asymptomatic person can still pass on COVID-19, as the virus is present in their system, whether it be in the respiratory tract or lungs, however, it would be harder to do so because they aren’t coughing.
“They still have to get that virus out and onto their hands or surfaces or into someone’s face,” he said.
“So it’s likely to be happening less often if they’re not productively coughing, or something else that would spit that out.
He added that there is a fair bit of the virus which shows up in saliva, and talking may be one of the ways the coronavirus is spread, because everyone “spits a bit” when they talk.
Prof Mackay explained on Facebook the timeline of how long someone with COVID-19 is infectious varies depending on how sick a person is.
“We know that people who go on to die, are positive of the virus right up until that point,” Prof Mackay said.
“We know that asymptomatic people or mild illness is positive for about a week after they generally are well, and people who have a more severe disease and are in hospital may be positive for up to three weeks.”
Prof Mackay then clarified what he meant by ‘positive’.
“I’m talking about bits of Nucleic Acid in very sensitive tests,” he says.
“We don’t know for sure if that always means infectious virus.”
Why some people don’t show symptoms
As for why some people are asymptomatic, while other suffer symptoms varying in severity, there is no clear indication as to why.
During his chat with Yahoo News Australia on Facebook, he said it wasn’t clear if genetics played a part in why someone will show symptoms while someone else might not.
“It’s very complex to prove genetic links and viral infection,” he said.
While COVID-19 does not discriminate, and anyone of any age can develop symptoms, many of the people who have died of coronavirus have been older.
However, Prof Mackay points out age may not be a contributing factor as to why a person is asymptomatic, saying people of all ages have displayed no symptoms yet tested positive or experienced only mild symptoms.
“I think anybody could be asymptomatic, even an older person,” he said, adding it was still a mystery as to why two people in the same age group suffer varying degrees of severity.
However, “viral load” may determine how sick one gets with COVID-19.
“How much virus you get exposed to initially, or it might be how often you’re exposed [to the virus]” he said.
Prof Mackay added there have been some studies which strongly suggest asymptomatic cases pass on the virus to other people, but mainly just people they have close and prolonged contact with.
“Not just someone who walked past them, or jogged past them,” he said.
“Someone who has had a fair bit of contact. That’s been the case throughout COVID-19’s development, it does take that close and prolonged contact before you pass on the infection.”
However, Prof Mackay says it is unclear how long someone has to be exposed to get the infection, or how much virus needs to be inhaled to get an infectious dose.
“That’s all up in the air really, so to speak,” he says, before reiterating the longer an infected person is with an un-infected person, the more likely it is the virus will be passed on.
He said face masks, may be beneficial for people who are not showing symptoms, yet there is a possibility they may have the coronavirus.
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