The term “viral shedding” has been discussed during the COVID-19 pandemic. Some discussions have left a wake of misunderstanding about how and when viral shedding occurs. So, let’s take a closer look.
Even though viruses can cause a lot of damage, they are typically very simple organisms. They often contain only a few proteins and either DNA or RNA, known generally as nucleic acids. The nucleic acids are instructions for making more viruses. But even with these instructions, viruses do not have everything they need to reproduce. In order to survive, viruses must infect another organism, such as a person. Once inside the organism, the virus must gain access to a cell , which has the necessary machinery and building blocks to make more viruses. By taking over the cell, the virus is able to redirect the cell’s activity for its own benefit — making more of itself to survive.
New viral particles that result from this process can go on to infect other cells, and with each round of replication, the number of viruses in the individual increases exponentially. The longer it takes for the individual’s immune system to recognize what is happening and gain control over this process, the greater the number of viral particles that will be produced and the greater the battle between the virus and the immune system that will occur. An infected individual will recognize this battle in the form of symptoms of illness — fever, fatigue, congestion, vomiting, diarrhea, etc. The symptoms will vary based on which virus it is and what type of cells it infects. In the case of SARS-CoV-2, the virus that causes COVID-19, the primary location of the early infection is the respiratory system, specifically cells that line the inside of the nose and throat.
As viruses are produced in the nose, they may gain entry to other parts of the body, where they can infect more cell types and cause additional symptoms or complications. But these newly formed viral particles can also have a second fate. They can leave the infected person in nasal and oral secretions. Viral shedding refers to this second fate. Because these viruses can go on to infect someone who is exposed to the nasal or oral secretions, viral shedding and the spread of disease are closely intertwined.
During the COVID-19 pandemic, viral shedding has been discussed in relation to masking and vaccinations.
Because a person infected with a respiratory virus is shedding virus particles from their nose and mouth, you can quickly conclude that a mask will decrease the spread of viral particles as they are physically trapped by the mask. This is why early messaging during the pandemic was that wearing a mask was a way to protect those around you. This became particularly important as we learned that people infected with SARS-CoV-2 can spread the virus a few days before they develop symptoms. The fact that SARS-CoV-2 can spread in the two to three days before a person feels ill makes it more difficult to contain compared with similar viruses, like SARS-CoV-1, which was first identified in China in 2003, and MERS-CoV, which was first identified in Saudi Arabia in 2012.
Two additional aspects of masking are worth considering in the context of viral shedding:
Viral shedding can occur following vaccination if the vaccine contains live, weakened viruses because that type of vaccine causes immunity through viral reproduction. Examples of routinely used live, weakened vaccines include measles, mumps, and rubella (MMR); chickenpox; rotavirus; and the intranasal influenza vaccines. The oral polio vaccine (OPV) also contains live, weakened virus. While OPV is no longer used in the U.S., it is still used in some other countries. The yellow fever vaccine, while not routinely used in the U.S., is also a live, weakened vaccine. The new COVID-19 vaccines being used in the U.S. do NOT contain live virus, so they are not capable of causing shedding, but we will get to that below.
An important distinction between a viral infection and vaccination with a live, weakened viral vaccine is the amount of virus that is shed. If vaccination causes shedding, it typically results in significantly lower quantities of virus being shed, and the shed virus particles are less likely to cause disease because they are the weakened form used to make the vaccine. However, a few exceptions exist. For example, if someone is immune compromised, they might shed virus for a longer period of time because their immune system has trouble stopping viral replication. For this reason, some people with immune-compromising conditions cannot receive live, weakened vaccines. Another consideration is that people not immune to the disease could get infected through viral shedding. Sometimes this is beneficial as in the case of the oral polio vaccine, which causes more than just vaccinated people to be protected against polio. This type of protection is called contact immunity. But on occasion, viral shedding can also result in an infection with symptoms, such as when an unimmunized person comes into contact with the chickenpox rash of a vaccinated person and develops a mild case of chickenpox.
Confusion related to COVID-19 vaccines has also involved aspects of viral shedding. The source of this confusion is twofold. First, people may not distinguish between the reproduction of a virus and the COVID-19 vaccines causing our bodies to produce the spike protein. Second, like the whisper-down-the-lane game, talking down the line further confounds the confusion. Let’s take a closer look:
In sum, viral shedding is an issue when someone is infected with the virus that causes COVID-19, but not when they are vaccinated against it.
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Viruses make copies of themselves in human cells and then spread to other people. This is the process of viral shedding. People who are sick with COVID-19 shed the virus from their noses and mouths. While we can't stop viral shedding, we can stop those viruses from infecting other people.Feb 16, 2022 more