On Tuesday, World Health Organization official Maria Van Kerkhove was engaged in a weekly Q&A session in which she discussed the ways SARS-CoV-2 is spread. In part of the wide-ranging discussion, Van Kerkhove repeated what has been clear from the time that the disease first began to ravage the area around Wuhan, China: Though COVID-19 is responsible for hundreds of thousands of deaths, and for serious lingering illness in millions of others, there are still many who become infected by the virus but display few or no symptoms.
In discussing these people—most of whom Van Kerkhove described as having mild symptoms—she also noted that a smaller group are “truly asymptomatic” and that when it comes to passing along the disease, contract tracing that leads back to these people is “very rare.”
And from that statement came a thousand misleading news reports that desperately need to be corrected.
Despite a lengthy series of statements that clearly placed the cases she was talking about as a subset of a subset of cases, both broadcast and online sites immediately seemed to run with the idea that it was “very rare” for people without symptoms to pass along COVID-19. And the reactions to that claim followed a predictable path from people shouting “game changer” to angry statements that there had never been a reason to close the economy in the first place.
But while what Van Kerkhove said may be technically correct—even if her statement was based on information that is currently unpublished and unreviewed—she most definitely did not say that people without symptoms cannot pass along COVID-19, or even that this is a rare event. In fact, past studies have indicated that fully half of people who catch COVID-19 catch it from someone who is not displaying symptoms.
The way that Van Kerkhove’s statement is being reported misses two important points: First, it’s confusing people who pass through the disease while remaining asymptomatic—that is, never displaying any symptoms—with those who are pre-symptomatic. Pre-symptomatic individuals have already contracted the virus, but they’re not displaying any symptoms of the disease … yet. These people will develop symptoms later.
Secondly, Van Kerkhove made it clear in her statements that most of the people who are generally placed in the asymptomatic box when the term is used in the media and casual discussion are not actually asymptomatic. They may not have a wracking cough or be struggling for breath, but they may have other symptoms such as nausea, aches and pains, or a sore throat.
These people displaying light symptoms, and even “non-typical” symptoms, seem to pass along COVID-19 just fine. More importantly, the people who are pre-symptomatic—those in the group who have become infected but whose symptoms have not yet appeared—appear to be the most contagious of any group. In some past studies of outbreaks in specific areas, a full 80% of cases could be traced back to someone who was not displaying clear COVID-19 symptoms at the time of contact.
As a disease primarily spread by respiratory droplets, it seems only logical that those in the phase of the disease where they are coughing frequently should be more effective spreaders. And that is probably true. But people running a fever and coughing also do a better job of wearing masks, staying home, and in general practicing social distancing. Those who are around someone coughing and clearly ill are also more likely to take precautions. Those who catch COVID-19 from symptomatic carriers are usually family members and others who are forced to remain in close contact with someone even though they are coughing, sweating, and clearly a hazard.
People catch COVID-19 from people who are not displaying symptoms for the simple reason that they are not displaying symptoms. They seem to be safe. But they are definitely, emphatically, not safe. This is the biggest reason why COVID-19 has been harder to control than the closely related virus that causes SARS. SARS victims tend to be most contagious about five days after symptoms appear. COVID-19 victims are most contagious in the days shortly after and the days shortly before the first symptom appears. Just about every “super spread” incident in the news, whether at a funeral, a pool party, or a choir practice, came from someone who was not displaying obvious COVID-19 symptoms at the time.
People who are not displaying symptoms can pass on COVID-19. Failure to take proper precautions around people who are not displaying symptoms makes them the most effective carriers of COVID-19.
Nothing has changed. Wear a mask. Maintain good social distancing. And please stay safe.