Have you heard the big WHO announcement? People who aren’t showing symptoms don’t spread the virus!
— Happy people everywhere right now
The WHO’s announcement that infected people who aren’t showing symptoms of COVID-19 aren’t spreading the virus has gone viral all over my feed. People are understandably thrilled by this news. The CNBC headline reads: “Asymptomatic spread of coronavirus is ‘very rare,’ WHO says”. If people without symptoms don’t spread it, then there’s no need for a bunch of masks and distancing. We can beat the coronavirus by just having obviously sick people self-isolate!
There’s one problem with all of the above: none of it is true.
The WHO did not announce that people without symptoms aren’t spreading the virus, and even what they did announce about “asymptomatic” spreaders — an announcement that was thoroughly misreported by the press in general and CNBC in specific — they’ve since scrambled to walk back.
But before I untangle this sorry mess, here’s what you need to know: Studies show 35 to 44 percent of SARS-COV-2 infections are caused by people who were not showing symptoms when they spread the virus.
So even if you don’t have symptoms, or if the people around you don’t have symptoms, you still need to practice social distancing and wear a mask. We still need to worry about spread from people who don’t have symptoms of COVID-19.
Anatomy of a science communications disaster
To understand the main problem with the WHO announcement, you first have to know that there are two types of coronavirus transmission involving spreaders who show no symptoms:
- Asymptomatic transmission happens when someone spreads the virus, but they themselves never develop symptoms.
- Presymptomatic transmission happens when someone spreads the virus before they themselves develop symptoms.
In both cases, someone who is not currently showing any symptoms is spreading the virus, but in the second case (presymptomatic) they will go on to develop symptoms at a later date. And in some cases of “presymptomatic” transmission, the spreader does actually have symptoms, but those symptoms are mild enough (e.g. slightly low blood oxygen levels) that even the person experiencing them doesn’t notice them.
What the WHO tried to tell everyone with its original announcement is that truly asymptomatic spread (i.e., the spreader has absolutely no symptoms and will never go on to develop them) is probably not the main driver of the pandemic, because it’s supposedly rare and doesn’t seem to cause secondary infections when it does happen.
For what it’s worth, even that fairly narrow claim is disputed by infectious disease experts.
Nor am I convinced by the data that @WHO provide as evidence that asymptomatic transmission is very rare. Their relevant quote is below. This is thin evidence for such a policy recommendation. The other data they allude to have not been released to the best of my knowledge. pic.twitter.com/u7vXkuXD6j
— Carl T. Bergstrom (@CT_Bergstrom) June 8, 2020
But then the media got hold of the announcement. By the time science reporters got done misreading “asymptomatic transmission” as “not showing any noticeable symptoms at the time of spread” and misinterpreting “not the main driver of the pandemic” as “this is rare and not worth worrying about”, we ended up where we are now.
So if you have friends and family who are rejoicing at the “news” that you can’t spread coronavirus unless you’re sneezing or feverish or coughing up a lung, please correct them. As far as we know, it is still extremely possible to get coronavirus from infected people who have no obvious symptoms and don’t know they’re sick. This dangerous error needs to be corrected whenever it comes up, because it’s causing people to abandon the precautions that are necessary to control the outbreak.