Tag Archives: Prevention

How to Limit Asymptomatic and Pre-Symptomatic Transmission of COVID-19

While the world grapples with COVID-19, there has been some good news with several countries reporting work on capacity building for eventual vaccines and vaccine testing trials.  China, at the time of writing, had reported a peak and decline of new infections.  Meanwhile some of the hardest hit nations in the EU also reported a drop in new cases.  How long can this last?  That is a question based on whether countries can find and deal with pre-symptomatic and asymptomatic carriers of the virus.

Most of the attention on COVID-19 has been towards curtailing the virus by self-isolation and medical treatment for symptomatic cases.  Yet the virus can also spread through asymptomatic and pre-symptomatic transmission.  The former, where an individual has the virus but shows no symptoms at all throughout the entire infection, is rare.  The individual who is pre-symptomatic shows no overt symptoms or mild symptoms that are ignored or underreported.  For those with allergies to pollen, for example, might report headache, watery eyes, stuffy nose, and other symptoms that are typical of allergy season, but some of which are also symptoms of the COVID virus.  If that individual typically has seasonal allergies, they might misidentify their symptoms and either provide a false positive case or go unreported until after full on symptoms force medical attention.

While an individual may show no symptoms, they are still infectious if they have the virus.  In fact, this is probably the primary means of infection in the case of China, where the virus started grabbing global attention.  One study estimated that 86% of cases in country were a result of infection by individuals who did not report symptoms.  Individuals who do not know they have symptoms can transmit the virus in much the same way symptomatic individuals do- by droplets.  The different is that pre-symptomatic carriers transmit by respiratory droplets, the fine mist and spittle that comes from vocalizations like singing and talking.  One study by the CDC looked at pre-symptomatic transmissions in Singapore and found that 10 such cases accounted for 6.4% of 157 cases in country.

The contamination could also occur by environment such as someone infected who uses a public facility or objects that spend lots of time close to the mouth.  Cellphones are one prime example- they are close to the mouth when someone is talking, and those with touchscreens are exposed to whatever the face and hands touch.

With this in mind, countries around the world have been trying to find ways to detect the virus.  The early nucleic acid tests had the problem of false readings and an error rate of anywhere between 30% and 50%.  The cause of these errors could have been the inability of the test to detect viral load levels due to sample sizes, testing complexity and error, or timing.  The current best testing method, PCR testing, still has a success rate of 80-85% in detecting the virus and had to be refined as the process itself is often multistage and requires lots of attention.

This gives some insights to the reports of potential reinfection and false negatives in China regarding their testing and subsequent reports of problems with exported tests.  At the beginning of the global pandemic, China had developed means to test for the virus, but was still uncovering new information about the virus and refining their methods.  Early tests were designed with imperfect information, giving rise to higher error rates.  Yet they were still focusing largely on symptomatic cases and not on asymptomatic or pre-symptomatic cases, which factored into the spread of the virus.

Another issue is that immunity to the virus is not known for sure.  Scientists studying SARS and MERS, both from the same viral family as COVID-19, found that SARS recovery provided immunity for up to a few years while MERS recovery provided protection for only a year.  As COVID-19 is recently been studied, it’s still undetermined whether someone gains immunity or for how long.  In some cases, it might not have been a false reading by reinfection that accounts for individuals recovering and getting infected again.

In summary, COVID-19 is most likely to spread due to pre-symptomatic transmission in which people who have the virus are not aware of it because they show either no signs or mild symptoms that could be mistaken for other ailments.  Current tests may provide false readings because of issues with sampling, operator error, or timing.  Lastly, for medical providers and professionals this is a threat to their ability to fight the virus as they could either miss potential carriers or become carriers themselves.

One way to fight the virus is to spend as little time around people so as to not catch or spread the virus.  The self-isolation is one way to help.  Yet this is a luxury those who work in the service sector and other customer facing jobs cannot afford.  Here the wearing of face masks is essential because it stops the transmission of the virus through droplets, whether formed in a sneeze or from respiratory activities.  Whether healthy or infected, this measure can help in limiting the potential for infection.  Lastly, donating needed supplies for first responders and medical professionals, such as N95 masks and other personal protection equipment is essential to keeping the rate of infection and transmissions down for both patients and medical staff.  I would add here that paying attention to how local government and hospitals utilize resources is highly important to morale and effective use of resources.  Many of our medical professionals are taking on extra shifts, being forced to go without needed supplies, and have their own health to be concerned about in addition to all those they help daily.  Its a difficult time for everyone, especially those who are on the front lines of this viral pandemic.


  • Wash your hands frequently for at least 20 seconds,
  • Stay inside if you can,
  • Use cloth masks and face coverings that wrap around the mouth and nose
  • Stay at least 6 ft away from others
  • Sanitize surfaces that are often touched, including your smartphones
  • Be considerate of those required to come to work in grocery stores and other essential services
  • Donate supplies to the hospitals and keep an eye on local government to ensure they are properly supplying our medical professionals
  • Even if you feel fine, treat yourself as if you could spread the virus and take precautions

There you have it.  Pre-symptomatic and Asymptomatic transmission of COVID-19 can be limited if greater attention is paid to limiting the vectors for transmission.  Many of these things are within individual ability to control, just assume that you can be infectious and act to avoid spreading the virus to others.

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