Viral load is simply the amount of virus in the body. This varies in different parts of the body, and can change over time. Recent studies have shown, for example, that the viral load in the lungs of COVID-19 patients is greater than that in the nose.
A patient’s viral load increases as the virus replicates and disease symptoms get worse, and then decreases as the patient recovers. So monitoring the viral load can give us a useful indication of how a patient’s infection is progressing.
The amount of virus that you’re exposed to at the beginning of an infection is something different, and this is called the ‘infectious dose’. Studies on other viruses such as the flu and SARS have shown that the higher the infectious dose (the more virus you breathe in), the greater your chances of having more severe symptoms.
With one small exposure, your immune system may be able to fight off the virus before you get sick, but with repeated small exposures (such as touching your face throughout the day) or one large exposure (an infected person coughing in your face), the virus may grow faster than your body can control.
We don’t yet know if this link between infectious dose and disease severity holds for COVID-19, but it may do, and that’s why it’s so important to maintain physical distancing and keep the initial exposure as low as possible.