Explainer
What does COVID-19 do to the body and what's it like to have the illness?
"Three weeks in hell" or a bad cold? What does COVID-19 feel like, what are the phases of the illness and how does your body fight back?
A cough, a clammy forehead, shadows on the lungs. Most people infected in the viral pandemic now sweeping the globe will come down with only a mild case of the mystery illness. Some won’t know they’ve had it at all. But when it's bad, it can mount an attack on the whole body – and start a storm in the lungs.
How it plays out depends on the two factors important to any invasion: the strength of your defences and the strength (or dose) of what you’ve been hit with.
Connor Reed, 25, knows well the racking cough and spiking fever of the illness now called COVID-19. He says he came down with it late last year in the centre of the initial outbreak, Wuhan in China. He still lives just a 20-minute walk from the wet market where it's believed the strain jumped from wild animals into humans.
At first, Reed seemed to just have a cold. A week on, then early December, he was already feeling better when a fever hit, and a cough. His whole body started to ache. Another week went by. He thought he was on the mend until the cough became deeper, seeming to settle at the bottom of his lungs.
"It was hard to breathe," Reed says. "Even walking to the bathroom, I felt like I was running out of air. My ears hurt from it, I lost my balance at times. It started to get scary, like the worst flu I've ever had."
Reed ended up in hospital and, after a full day of testing, he says doctors told him he had a "new kind of pneumonia". Fortunately, he was fit and healthy: his life didn't appear to be in danger. Steroid inhalers helped reduce inflammation in his lungs and, more than a month after that first sniffle, Reed recovered. When he called the hospital in early January to ask more about his test results, they told him what was about to hit headlines around the world in just a matter of days – a new kind of coronavirus had been identified in humans. Reed was one of the earliest suspected cases.
Four months on, what do we now know about COVID-19 and how the body reacts? What is treatment like? And how long does recovery take?
Connor Reed, 25, in Wuhan, China. Having recovered from one of the earliest suspected cases of the coronavirus COVID-19, he is hoping to return to Brisbane, Australia.Credit:Facebook
How does the coronavirus infect a person?
You can’t see the virus with the naked eye – it’s nanometres wide. But when someone is infected, they can shed it, shooting viral particles at least a metre into the air in water droplets from their nose and mouth, usually through coughing or sneezing. Viruses infect a new host by harnessing our own cellular machinery to replicate. To get in, they need the key – a receptor within a cell they can bind to. Which cell a virus latches onto largely determines where it will spread throughout the body – and helps guide treatment.
The four main coronaviruses found in humans tend to colonise only the nose and throat. Collectively, they cause about one in four cases of the common cold and symptoms are mild: a runny nose, a sore throat, sometimes a cough or a fever. But since 2003, three dangerous coronavirus illnesses have emerged in humans: SARS (Severe Acute Respiratory Syndrome), which also spawned global panic when it exploded onto the scene 20 years ago, the more deadly but less common MERS (Middle East Respiratory Syndrome) and now the latest, COVID-19, which has already infected about 1.5 million people and killed about 87,000.
All three attack the lungs as well as the sinuses, sometimes developing into viral pneumonia – and, because they're new, there's little natural immunity to fight them off. COVID-19 is about 75 per cent similar to the SARS strain, and even thought to bind to the same cell receptors (ACE2), which are largely found in the lungs.
Early studies suggest this virus might be better at hacking into that receptor than SARS, which is why it's more infectious, says Professor Sharon Lewin, director of the Peter Doherty Institute for Infection and Immunity. A spokesman for the Australian Department of Health offered a different theory: the new virus appears to be replicating fastest in the nose and throat, rather than the lungs. That could make it more transmissible but also perhaps less fatal than the other two coronavirus outbreaks.
How do you test for it?
To find the virus, doctors need to catch it in the act, either by swabbing a sample directly from the nose and throat or in lung phlegm or by singling out the body’s immune response to the infection in a blood test.
The new strain has already been found in the lungs, nose, throat, even in faeces, says infectious disease expert Professor Raina MacIntyre. It can hitch a ride in the bloodstream to other organs such as the kidneys, liver, intestines and possibly the heart, brain and central nervous system, too.
But both methods of testing can return false negatives - a throat or nasal swab can miss the virus (because it's actually replicating lower down in the lungs) and a blood test, which is not yet widely available outside of China, can be performed too early - some people will take up to 9 days to produce antibodies to fight off a virus.
Professor Lewin adds, "Early on, you had doctors in China diagnosing just off chest scans because you can see that lung inflammation, even if it's not severe." Now, Sydney scientists have developed a fast training tool to help frontline healthcare workers spot COVID-19 in lung scans.
Still, infectious disease physician and microbiologist Professor Peter Collignon says it’s not yet clear if everyone gets the new virus in their lungs. “Finding it down there isn't a tipping point [for severity] by any means. Some children have it in their lungs but display no symptoms," he says. "But it might not have travelled all the way down from the upper respiratory area in every case."
What are the symptoms and phases of the illness?
Much of what we know about COVID-19 comes from studies of the first 55,000-odd cases in China, which found more than 80 per cent of people could fight off the illness without serious complications, even if they developed pneumonia. Lungs cleared, coughs eased and fevers broke. Anecdotally, some people have likened the infection to "three weeks in hell", racked by chills and struggling to breathe, while others have reported only a sore throat, a small cough, even no symptoms at all.
The main symptoms of the coronavirus
Based on data collected in China, most patients seem to have:
- Fever (88% of patients)
- Cough (68%)
- Fatigue (38%)
- Shortness of breath (19%)
A patient might also complain of chills, headaches or a sore throat, and nausea or diarrhoea have also been reported, though not in the numbers seen during SARS. Less than five per cent of cases so far involve a blocked nose.
With early symptoms deceptively similar to the common cold or flu, one sign of infection may be a loss of smell (and an accompanying reduction in taste), as the virus attacks that part of the respiratory system. Sometimes people infected with the virus who otherwise feel fine will find they cannot smell as usual - though experts say the effects are not permanent and the sudden loss of the sense is far from a "test" for the virus. (Not all patients report losing smell and the symptom is also associated with other common colds and viruses).
In the case of COVID-19, Professor Collignon says patients generally appear to have mild symptoms for the first week or so. In severe cases, they can intensify into pneumonia during the second and, in rarer cases, the infection will turn unexpectedly deadly.
At the World Health Organisation, assistant director-general Bruce Aylward warns when danger strikes, it's often fast-moving. Doctors report patients can go downhill quickly during those "critical" second and third weeks and urge people with or suspected to have the virus to monitor their symptoms, particularly their breathing and fever. Infectious diseases physician Sanjaya Senanayake says he's seen patients develop "bad shortness of breath" around the second week of symptoms. "Then if they're going to get very sick, about two and a half days later, they [usually] start to develop fluid in their lungs."
CT scans from a 77-year-old man with COVID-19 in China over 10 days, showing ground-glass opacity of the lungs and lesions. The man died 10 days after the final scan.Credit:The Lancet medical journal
What can go wrong during the infection?
On scans, they call it ground glass – a white mist over the usual empty black of the lungs. In some cases, there are bright spots, eerily similar to the “honeycomb-shaped” lesions left by SARS, but mostly COVID-19 makes a finer and more-even pattern across both lungs. This inflammation is a sign the body is fighting back against the virus – in that battle, the lungs are ground zero. But Professor Collignon warns sometimes the collateral damage can be worse than the bug itself.
As the immune system ramps up its defences, blood vessels start to leak and the lungs can be flooded with cellular debris, making it harder for them to pump oxygen to the rest of the body – and harder for patients to draw breath. "They start to drown," Professor Collignon says.
Falling blood oxygen levels put pressure on other organs, in particular the heart. More systems can start to fail, and blood pressure too, which, if it falls low enough can tip the body into septic shock, a whole-body infection.
"Even if the virus spreads to the heart or the kidneys and damages them, the real cause of death is still probably going to be oxygen levels falling and setting everything else off," Professor Collignon says. "If you're an older person or already unwell and those organs are weaker, it can be the straw that breaks the camel's back."
While there is a theory that people with already compromised immune systems might escape this effect and so cope with an infection better than expected, Professor Collignon warns they are especially vulnerable to the other big killer – co-infection.
Usually being hit with two bugs at once is rare, though not impossible. But as the virus chews through cells, it leaves the lungs less able to filter out germs picked up from the nose and throat – and wide open to a case of the flu or even a bout of bacterial pneumonia. (The first man to die from COVID-19 in Thailand was also sick with dengue fever.) During the deadly 1918 Spanish Flu pandemic, most victims died not from the original virus but due to these second-wave bacterial pneumonia infections. Fortunately medicine has advanced a lot since then, making such complications much easier to treat.
So who is at risk of serious complications?
So far, the WHO reports about 20 per cent of cases become severe, requiring medical intervention for serious breathing difficulties and falling blood oxygen levels. Of those, 6 per cent have been pushed into critical care – as multiple organs begin to fail alongside the lungs or septic shock sets in. About 3.4 per cent have died. But experts expect the real death rate is actually much lower, given so many mild cases will likely go undiagnosed.
While anyone can catch the virus, older people and those with other conditions such as diabetes or heart disease are most at risk of fatal complications. ("Over the age of 50, the immune system starts to fall apart," Professor MacIntyre explains). But in Italy, where the virus has gained a particularly deadly foothold, doctors warn that younger patients (in their 30s, 40s and 50s) were also presenting to overwhelmed emergency departments needing help to breathe. Some have even raised the prospect of an age limit for intensive care to free up beds for younger cases as life-saving machines such as ventilators become worth their weight in gold.
Data since complied from elsewhere in Europe and North America also reflects a concerning number of hospitalisations among people under 55, prompting warnings for younger adults to take COVID-19 more seriously. As of April 6, 448 of Australia's then 5795 cases were in hospital, 96 of them in intensive care. Deputy Chief Medical Officer Paul Kelly said many of those people were young - in their 30s. "This is not just an old person's disease," he said. "Those young people don't have [other] risk factors." While so far those who have died in Australia have been over 50, people in their 20s have seen the highest number of coronavirus infections of any age bracket.
So far internationally very few children have been diagnosed or suffered serious cases globally – a phenomenon also observed during SARS. Still, they are not immune and some have died from the illness, including the heart-breaking case of a six-week old baby in the US.
Smokers are considered more at risk, as early studies show the same cell receptors the virus hijacks in the lungs increase with cigarette smoke. But pregnant women and breastfeeding mothers so far do not appear in any heightened danger, as they were during the last pandemic, the 2009 swine flu. Still they should take precautions as they are known to be more susceptible to other common respiratory viruses.
Whatever your personal vulnerability, the dose of virus you first receive – say, from touching a contaminated door knob versus caring for an infected person over several days – also plays a big part in how your body copes. "The higher the dose the faster you will get sick, and the harder it will be on you," Professor MacIntyre says.
That could explain why otherwise young and healthy medical workers have died from the disease. Li Wenliang, the 34-year-old doctor who blew the whistle on early cases of COVID-19, went through a gamut of treatments after falling ill himself, including antivirals, antibiotics, even having his blood pumped through an artificial lung, but he died weeks later. As with SARS, clusters of severe infection are emerging in hospitals and households as people come into sustained close contact.
How do doctors treat the coronavirus?
Despite the breakneck speed of global research, a vaccine for COVID-19 is still many months away. And, while antivirals and therapies that block diseases such as malaria, Ebola and HIV are being trialled against the new disease in some parts of the world, including Australia, treatment is largely about managing complications – providing oxygen, keeping up fluids and monitoring how the body is coping. Antibiotics don't work on the virus as it is not caused by bacteria but they can be deployed against secondary infections. If breathing starts to fall, respirators and other measures will kick in to keep the lungs going.
As Professor Lewin explains, doctors have a key choice when treating any new virus: is it better to block it directly with antiviral therapies as in the case of HIV or should they also dampen down the body's immune response using drugs such as Interferon, to minimise the fall-out damage?
"Sometimes that can help but sometimes it means the infection overwhelms," Professor Lewin says. "It didn't work with SARS but there's been some success with MERS. Already for this, there's been candidate [therapies] that look good in test tubes, but we need trials. China has about 70 going, testing different [approaches] but they're actually struggling to enrol people now as cases fall."
No vaccine exists for either SARS or MERS - the former died out within about nine months so an inoculation never hit the market while the less common MERS has struggled to attract research funding since it emerged in 2012. After the big Ebola outbreak of 2014, a global group formed to speed up research into vaccines and MERS was recently identified as a priority. "Then this new one hit," Professor Lewin says.
Professor Collignon thinks it unlikely any of the potential treatments now being tested against COVID-19 will save the day before a vaccine hits the market – without larger trials, he warns, small studies can miss big problems on roll-out. Experts also warn of increased pressure on hospitals if severe coronavirus cases hit wards all at once. While Australia's healthcare system is strong compared to other countries, it's population is also older, Professor MacIntyre notes, meaning more demand for intensive care. To slow down the virus and avoid a "pinch" around flu season, Australia has followed other countries in rolling out stricter containment measures such as quarantining suspected cases, shutting down gatherings and ordering people to stay home except for essential reasons. So far it appears to be working - a surge in new infections in mid-March has now begun to flatten.
What happens in intensive care wards?
Most people with COVID-19 present to hospital because they're having trouble breathing, says the head of the Alfred Hospital’s intensive care unit, Associate Professor Steve Mcgloughin. Once admitted and getting oxygen via a mask, a person’s condition may improve – but others will need ventilators or other machines to keep their lungs and organs working.
Anyone who’s had a general anaesthetic will have relied on a breathing machine known as a ventilator, whether they know it or not. But Dr Suzi Nou at the Australian Society of Anaesthetists says that while a patient having routine surgery will need a ventilator for minutes or hours – perhaps a few days in intensive care – a patient with COVID-19 might need one for as long as 10 days.
Australia is already doubling the number of ventilators (and intensive care beds to go with them) in Australia to 4000 - some are being freed up by the suspension of non-urgent elective surgery. But behind every ventilator is a team of experts too, such as Dr Nou. It's those doctors and nurses who will need help to keep coming to work in the weeks and months ahead, says the head of the Alfred Hospital’s intensive care unit, Associate Professor Steve Mcgloughin. "Everyone is very focused on the machines," he says, "but the most valuable resource we have in healthcare is the people." Retired healthcare workers as well as medical students are now being drafted into the fight.
Dr Mcgloughin, who chaired the group that wrote the COVID-19 guidelines for The Australian and New Zealand Intensive Care Society, says Australian hospitals are benefiting from the advice of colleagues overseas, including in Italy and Singapore, both about treatments and how to protect themselves.
“Within weeks of what happened in Italy, they had already published very detailed summaries of what happened. I’m amazed the guys were able to do that.”
How long does recovery take and is the damage permanent?
Professor MacIntyre says it's too early to say if this disease will result in any permanent damage for severe cases– such as the lung tissue scarring seen in some SARS and MERS patients. But a full recovery typically takes about 10 days to a month. Symptoms tend to clear up within a fortnight in mild cases or six weeks for more serious, Associate Professor Senanayake says.
Australian researchers have now mapped the body's immune response, identifying the antibodies it recruits to defeat the new virus, in some people starting the fight within just three days of the initial infection.
What about immunity?
So far, more than 300,000 people have already recovered worldwide. With these virus-fighting antibodies in their system, many experts expect they will remain immune for some time, though it is unclear for how long. Recovering from a virus usually confers at least a period of immunity (though not always a life-long shield). Common coronaviruses such as the ones that give you a cold tend to go away for at least a year or so before we become susceptible again. Studies of MERS-CoV has found antibodies still present in survivors more than 18 months after recovery, and some survivors of SARS retained antibodies for many years thereafter.
For COVID-19, there have already been cases of people cleared of the virus, only to test positive again days later or, in the case of one woman, more than a month down the line. But while experts say it's possible to be re-infected again, it's more likely the virus was still in their system. Some studies have even suggested it can lie dormant in other parts of the body for weeks - with the longest period of infectiousness recorded as 37 days so far. "But in some cases, when people are returning persistently positive tests after getting better, they might be finding dead virus," Associate Professor Senanayake says.
Amid a shortage of testing kits world-wide, Australia is only retesting frontline staff in health and aged care to confirm their recovery. That means official recovery data remains patchy. Most patients are instead told to wait 72 hours after symptoms disappear (provided they have already isolated for 10 days from illness onset).
A federal government spokesman also said a patient who keeps testing positive after symptoms vanish is not necessarily still infectious. "There have been case reports of patients testing positive for a couple of weeks post-symptom resolution, but are viral culture negative meaning they are unlikely infectious for very long after symptoms resolve," he said.
Back in Wuhan, Reed was cleared to leave his own home quarantine months ago but, like tens of millions of people in China, he'd spent the first three months of 2020 under lockdown in an unprecedented government effort to stem the virus's spread. On April 8, the streets finally opened again - residents waved flags and sang songs as they left their homes for the first time in 11 weeks. While the local government did not appear to pick up early cases of the virus, Reed says China took the right step, however extreme, in shutting down parts of the country - the government's data says new infections have all but stopped within its borders, even as new frontiers of the virus rage in the US and Europe.
"In Italy, it seems to be a similar thing to Wuhan," Reed says. "The virus was there, but people didn't notice, it was brewing quietly for a while, and then it suddenly exploded. Now they've followed China with lockdowns. Australians need to take this seriously."
Reed was born in the UK but is now hoping to return to Brisbane, where he grew up and his family still live. "I'm likely immune now, I feel fine, but I know I've gotten very lucky. "
If you suspect you or a family member has coronavirus you should call (not visit) your GP or ring the national Coronavirus Health Information Hotline on 1800 020 080.
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With Felicity Lewis
This article was originally published on March 13 and has been updated to include new research.
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