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Coronavirus: What is viral load and does it affect how sick COVID-19 patients get?

Viral load is the numerical expression of the quantity of virus in a given volume of fluid.
Viral load is the numerical expression of the quantity of virus in a given volume of fluid. Copyright Pixabay
Copyright Pixabay
By Emma Beswick
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Is it as cut and dry as the more viral particles a person is exposed to when they are infected with COVID-19, the worse they will feel? Euronews breaks it down.


"Viral load" has become a buzzword since the beginning of the coronavirus pandemic. But what does it actually mean?

In short, it is the numerical expression of the quantity of virus in a given volume of fluid.

But is it as cut and dry as the more infectious viral particles a person is exposed at the point of infection (the inoculum), the worse they will feel?

And to what extent does viral load affect how easily someone can catch and spread the virus?

How does viral load work when infecting people?

The World Health Organisation says the coronavirus can spread from an infected person’s mouth or nose in small liquid particles when they cough, sneeze, speak, sing or breathe heavily. Current evidence suggests that the main way the virus spreads is by respiratory droplets among people who are in close contact with each other.

"It's a numbers game," Professor Stuart Neil, head of the Department of Infectious Diseases at King’s College London, told Euronews.

"If you breathed in a million virus particles rather than 100,000 virus particles, then you are very roughly 10 times more likely to get infected."

"The more infected cells you have, the more damage the virus does, the more inflammatory response it induces and the sicker you feel," he added.

But he cautioned that this relationship was not "a straight line correlation" as factors like not all virus particles being as infections as others make the calculation more complicated.

If you got the virus by touching something with particles on it and rubbing your face, your exposure to the inoculum is much lower than if someone in an intensive care unit who had COVID-19 coughed in your face, for example.

Neil added that this knowledge of the virus is based on experimental systems carried out in a laboratory and said how virus transmission plays out in real life is difficult to replicate fully in an artificial environment.

Does a greater viral load lead a COVID patient to have more severe symptoms?

While articles and studies have linked viral load to mortality, Neil doesn't think it can be connected to symptoms in such a direct way.

"There is not a great correlation between how much virus you can detect and how sick someone is," he said.

"There are plenty of examples of people who have quite high viral loads and are relatively asymptomatic," he argued.

"There's no straight line to say if you get this amount of virus, you will get this sick, it doesn't work like that."

Although, Neil went on to explain that if you get a bigger inoculum, you might be more likely to be sick, as the speed at which the virus replicates could be attributed to this.

What can I do to reduce the number of particles I'm exposed to?

"Every little barrier you put in the way achieves something," explained Neil, referring to mask-wearing, hand washing, social distancing and other measures to combat COVID-19.

He said that by sitting next to someone rather than opposite them and opening windows to disperse particles you can decrease the viral load you get from an infected person.


However, nothing is as effective as not seeing someone face-to-face and no physical contact; without these methods, you can't reduce the risk of catching COVID-19 to zero, he explained.

Neil added that even the vaccines that are currently being rolled out across Europe aren't a silver bullet for stopping transmission, as we don't yet know how they stop people from being infectious to others and we won't "for some time".

"People who have had the vaccine, especially if they have only had the first dose, shouldn't assume all bets are off and fully safe to others," he said.

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