Coronavirus: Amount of particles, or 'viral load' affect severity

Professor Lucy Yardley, from the University of Bristol, sounded the alarm today, saying evidence shows ‘viral load’ plays a big role in how sick someone will become

People exposed to a higher dose of coronavirus are more likely to fall critically ill, a scientist part of Number 10‘s SAGE panel has warned.

Professor Lucy Yardley, from the University of Bristol, sounded the alarm today, saying evidence shows ‘viral load’ plays a big role in how sick someone will become.

She said it explains why so many healthcare workers – who come into face-to-face contact with gravely ill patients – have fallen victim and died from the disease and should be factored into ministers’ lockdown exit strategy.

Having a high viral load – the number of particles of the virus they are first infected with – gives the bug a ‘jump start’.

It also raises the risk of a patient’s immune system becoming overloaded in its battle against COVID-19.

It means someone infected indirectly by touching a door handle could end up with milder symptoms than someone who inhales an infected person’s cough.

Professor Yardley warned the virus could be deadlier if it spreads between families in the same house because of the prolonged close contact. She didn’t mention whether co-workers would be at risk – but they would also come into contact with each other in the office without strict social distancing rules.

Having a high viral load – the number of particles of the virus they are first infected with – gives the bug a ‘jump start’. It also raises the risk of a patient’s immune system becoming overloaded in its battle against COVID-19. It means someone infected indirectly by touching a door handle could end up with milder symptoms than someone who inhales an infected person’s cough

Repeated exposure to high viral load explains why so many healthcare workers have fallen victim to the disease. Pictured: Staff in PPE treat a COVID-19 patient at the Royal Papworth Hospital in Cambridge

She told the BBC Radio 4 Today programme this morning: ‘There’s a lot of suggestive evidence that the more virus that you’re exposed to while you’re becoming infected, both the higher risk you’ll become infected but also you might be more severely ill.

‘And I think this is behind the recommendations for, of course, lots of protective equipment for people that are exposed to a lot of the virus in hospitals and now in care homes.

WHY DOES A HIGHER VIRAL LOAD INCREASE SYMPTOMS?

Everybody who contracts COVID-19 will develop huge amounts of the virus inside their body, but people will become first infected with different quantities of it – known as a viral load.

Someone who breathes in the cough of a seriously ill patient in the height of a fever, for example, will be exposed to more of a virus than someone who touches a door handle that was coughed on two days ago.

Most of the coronavirus symptoms are caused by the immune reaction which is triggered when the virus is discovered in the body.

In a bid to destroy the viruses the body ratchets up its internal temperature to kill them, causing a fever, and uses huge amounts of calories to send immune cells out into the blood to attack the viruses, causing tiredness and aching.

Being exposed to a smaller number of viruses at the start may mean the body can start off with a smaller immune response.

More viruses, however, would mean a need for a bigger reaction which could produce worse symptoms and then raise the risk of it tipping over into sepsis later on in the illness.

‘But we’re arguing that that probably needs to be applied more in the home as well, where people are caring for most of the people that are ill with coronavirus.

‘It’s kind of been observed mainly in places like hospitals – but actually you do see whole families going down with it very badly as well.

‘People actually worry, possibly too much, about passing somebody on the street without a mask [but] unless they cough in your face, which would be dangerous, that’s probably not very risky.

‘Whereas, having to spend a considerable amount of time close by to someone, that is a particularly risky situation.’

The professor of health psychology said there were ways to effectively avoid catching the bug even if someone in the same home is infected.

She added: ‘You really want to isolate from them as much as you possibly can, so if you have more than one room in the house then really you need them to be in a room completely on their own and not coming out into the kitchen.

‘If you can have different places to wash and so on, that would be good. If you can’t, then you need to have very good cleaning of all the taps and shared surfaces immediately [after] they’ve used them, good ventilation in the home so that any germs that are circulating go to the open air.

‘There’s a whole number of things that you can and need to do. People tend to think it’s inevitable we’ll get it… you really can reduce the number of infections in the household by doing all of this.’

‘If there is a safe place you can go to in another house, if you know somebody else that has a room you could safely use, that would be very helpful.

Fallen heroes: Pictured are the faces of some of the frontline health and social care workers who have died with coronavirus during the pandemic

How many medics have died from coronavirus?

The Government says that 49 NHS staff have died from COVID-19, but it is clear that many others have died.

Figures suggest that at least 171 frontline healthcare workers have fallen victim to the disease.

They include at least 27 doctors and around 100 nurse and healthcare supporters, according to Nursing Notes, a website devoted to the welfare of medical staff.

But the true figure is likely to be higher because not all deaths will be in the public domain and not all victims will have been tested for the illness.

And official NHS data last month found one in three frontline workers had tested positive for the disease.

Out of 17,000 swabs carried out on key workers on April 14, 5,733 people were positive – a rate of 33 per cent.

It suggests that infection was rife in UK hospitals – where staff have consistently struggled to access protective equipment – at the peak of the crisis.

In Italy, at least 101 medics have died from coronavirus, including 80 doctors and 21 nurses.

An additional two nurses took their own lives since the outbreak.

Professor Yardley has laid out these recommendations to ministers in a commentary which has been submitted to the prestigious British Medical Journal to be published tonight.

The report, also advises the Government to use positive messaging to encourage Britons to adhere to social distancing when restrictions are eased, as opposed to a fear-driven campaign.

The way viruses make people ill is by multiplying rapidly once inside the body and building up in such large numbers that the body takes weeks to destroy them all.

This process is inevitable once someone has caught an infection, but it is possible for people to first become ill with only a small dose of a virus.

This can, in theory, make it easier for their body’s immune system ‘army’ to cope and to fend off the early infection.

In fact, for coronavirus, it seems likely that a large majority of patients become ill under this circumstance and take an unusually long time to notice they’re sick.

Because of this, people appear to be spreading COVID-19 more widely than they would if they had a more serious disease.

Dr Michael Skinner, also from Imperial College, said that if someone starts off with a massive amount of the virus it could overload their immune system.

The virus would get a ‘jump start’ in such circumstances, he suggested, because it would be able to build up faster before the body had time to respond.

Dr Skinner said: ‘We must be more concerned about situations where somebody receives a massive dose of the virus (we have no data on how large that might be but bodily fluids from those infected with other viruses can contain a million, and up to a hundred million viruses per ml), particularly through inhalation.’

He said that this would be a ‘rare event’ and it was unlikely that people outside of hospital staff would be exposed to massive amounts of the virus.

Scientists do not think that people’s viral load will increase if they are exposed to more infected people after they first become ill themselves.

Nor do they think there is not likely to be a build-up of the virus from multiple sources before it reaches a threshold that makes them ill.

Dr Skinner added that if someone is infected with a large viral load: ‘The virus receives a massive jump start, leading to a massive immune response, which will struggle to control the virus to allow time for acquired immunity to kick-in while at the same time leading to considerable inflammation and a cytokine storm.’

Uncontrollable inflammation (swelling) caused by the body’s immune system can be devastating and cause deadly conditions such as kidney failure or sepsis.

It is known to be a contributing factor to severe illness and death among COVID-19 patients.

And a ‘cytokine storm’ happens when white blood cells go haywire and can cause kidney or lung failure and death.

Professor Jonathan Ball, a virology expert at the University of Nottingham said: ‘It is possible that individuals with pneumonia who have a higher viral load might develop more serious disease, but disease development is complex and no doubt many factors will have an impact.’

HIGHER VIRAL LOAD LINKED TO MORE SEVERE SYMPTOMS, STUDY IN THE LANCET FINDS

A scientific paper published in British medical journal The Lancet in March suggested that a high viral load was linked to worse symptoms.

The study looked at 76 coronavirus patients in Nanchang, China, who had been admitted to hospital and tested positive for COVID-19.

The researchers, led by Dr Wei Zhang, wrote: ‘The mean [average] viral load of severe cases was around 60 times higher than that of mild cases suggesting that higher viral loads might be associated with severe clinical outcomes.’

At least 80 per cent of coronavirus patients are believed to have only a mild illness similar to a cold, while some might develop more severe breathing problems.

The most seriously ill end up in hospital with pneumonia and in intensive care units have a survival rate of around 50 per cent.

Dr Wei and colleagues added that high viral load also seemed to raise the risk of a serious illness in patients with SARS, a similar virus that caused an outbreak in 2002.

They wrote: ‘This finding suggests that the viral load of SARS-CoV-2 might be a useful marker for assessing disease severity and prognosis.’

Researchers at the University of Oxford agreed that studies seem to show that a higher viral load makes coronavirus symptoms worse but there was no solid proof.

An analysis by the Nuffield Department of Primary Care Health Sciences reads: ‘The evidence suggests an association of viral dose with the severity of the disease.

‘However, the evidence of the relationship is limited by the poor quality of many of the studies’.

To avoid becoming infected with a larger viral load the best thing people can do is to stay away from others who are or might be ill, Dr Wendy Barclay said.

The viral load would be higher if someone coughed directly into your face than it would if they were two metres away and the viruses were dispersed in the air.