Why It Matters How Much Virus Is in the Body
New data suggests that viral load might be an important factor for transmission and disease severity
Once a virus infects a body, it starts replicating. The amount of virus a person has inside of them — and the amount of virus that person is producing — is what’s referred to as viral load. For many viruses, the higher the viral load, the worse the disease. Scientists are still learning the implications of a high viral load of SARS-CoV-2, the virus that causes Covid-19, and new research is beginning to provide some insights.
Understanding viral load is important for a couple reasons, experts say. “The first is that presumably if your viral load in the upper respiratory tract is high, the combination of that and the amount and types of respiratory droplets that you are expelling is what we think contributes to the likelihood of transmission of Covid-19 from one person to another,” says Abraar Karan, MD, MPH, an internal medicine doctor at Brigham and Women’s Hospital and Harvard Medical School. “If you have a low viral load, presumably even if you are expelling many droplets, each droplet has a lower concentration of viral particles and is less likely to cause a clinical infection in someone else. We are still understanding what this threshold is, but the general concept holds.”
A recent study published in the journal JAMA Internal Medicine looked at over 300 people with Covid-19 in a community treatment center in South Korea and found that the people who were asymptomatic had viral loads (the amount of virus in their nose, throat, and lungs) that were similar to people with Covid-19 who had symptoms. This could mean that people with symptoms and people without symptoms may spread the virus similarly since they carry it at fairly equal levels. However, people without symptoms are less likely to cough and sneeze, and therefore it’s possible they don’t spread the virus as effectively even if they have high levels of SARS-CoV-2. More research is needed.
There’s also the question of whether a higher viral load of SARS-CoV-2 means a person could experience a more severe infection than someone with a lower amount of virus. “The more virus that has spread to different organs in different parts of the body, the more…