Asymptomatic shedding of viruses is the norm

*edited to be more clear about relationship between shedding and contagiousness

Recently, there’s been scientific and media attention on how people can spread COVID-19 without showing symptoms. This is obviously a public health threat. However, this is also something that really should not be news.

Most infectious viruses can be spread without people showing symptoms. Symptoms are mostly what happens when the body’s immune system starts ramping up a fight against a virus. Symptoms do not indicate the virus itself.

Let’s take 4 examples for this, one from each of the major virus classifications: herpesvirus from enveloped DNA, adenovirus from nonenveloped DNA, influenza virus from enveloped RNA, and rhinovirus from nonenveloped RNA.

In herpes: “transmission of genital herpes in most study subjects (37 [56%]) appeared to have resulted from sexual contact in the absence of lesions…” (JID, 2008).

In adenovirus: “52% of asymptomatic children recruited from an Alaskan community tested positive for shedding respiratory virus in a one-time sampling scheme, with the majority having HRV and adenovirus.” (J Med Virol, 2010).

In influenza: “25 (11%) of asymptomatic cases displayed virus shedding” (Clin. Infect Dis., 2017).

In rhinovirus: “Rhinovirus can be detected in 15% of asymptomatic children” (Clin Micro and Infect, 2013).

It should be presumed that most viruses follow the same pattern. If someone is infected or shedding the virus, they can likely transmit the virus. It might not be easy, if it’s not a very infectious virus, but it can probably still happen.

More broadly speaking, this is an annoying pattern I’ve noticed with discussion and research into COVID-19 in general. It is a virus like any other. It broadly follows the same patterns we’ve seen with other viruses, especially other enveloped RNA viruses like the flu. The details of it are different, so it’s had a broad impact, but there’s no need to throw out prior research.

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