How ‘Stealth transmission’ is fueling the rapid spread of Covid-19, according to experts

The Covid-19 outbreak in the United States has snuck up on most of us like a waking nightmare. No one expected or wanted to believe the situation would escalate to this point. Today, the nation and the world as a whole wake up to a sea of uncertainty; what will our economy look like in six months? How about our social lives? 

It’s OK to feel scared, but all hope is not lost. This virus isn’t unstoppable, as evidenced by the considerable progress being made in China. Together, we will overcome this setback. In the meantime, though, perhaps our strongest asset in this fight is accurate information.

To that end, a new study just released by Columbia University is providing some much-needed clarity on how Covid-19 has spread so quickly and thoroughly all over the world.

What researchers have found out about ‘stealth transmission’

Researchers from Columbia’s Mailman School of Public Health have found that the initial rapid outbreak of Covid-19 in Wuhan, China was caused in large part by asymptomatic or undetected carriers. It’s the Coronavirus’ penchant for “stealth transmission” that has made it so hard to contain. It’s incredibly hard to stop an emerging pandemic when the majority of carriers have no idea they’re contagious.

“The explosion of COVID-19 cases in China was largely driven by individuals with mild, limited, or no symptoms who went undetected,” says co-author Jeffrey Shaman, Ph.D., professor of environmental health sciences at Columbia University Mailman School, in a press release

These findings make a world of sense in regards to America as well. While there were a relatively small number of Covid-19 cases reported in the United States in January and February, most people read the news headlines and carried on with their lives. Unfortunately, the virus has been spreading under the radar all over the United States over the past two months, hitching a ride from person to person. Some of these carriers may have simply assumed they were dealing with a cold, while others may have shown no symptoms at all.

This certainly isn’t to say Americans, or any other nation’s citizens, acted stupidly. No one was prepared or fully understood the scope of Covid-19’s contagious properties. We’re all playing catch up. 

The study’s authors used a computer model of the outbreak in China between January 10th-23rd and January 24th to February 8th to come to their conclusions. In all, they estimate that 86% of all Chinese infections went undetected or undocumented before the official Wuhan travel lockdown on January 23rd.

“Depending on their contagiousness and numbers, undetected cases can expose a far greater portion of the population to the virus than would otherwise occur. We find for COVID-19 in China these undetected infected individuals are numerous and contagious. These stealth transmissions will continue to present a major challenge to the containment of this outbreak going forward,” professor Shaman notes.

On a per-person basis, undocumented, asymptomatic, or presymptomatic infections are believed to be roughly 52% as contagious as individuals with severe symptoms. However, those undetected infections in Wuhan are believed to have caused two-thirds of documented infections. In short, it wasn’t the people with obvious symptoms driving the virus’ initial spread in China. Undetected cases fueled the outbreak and even caused the majority of severe infections that ultimately required hospitalization.

Now, here’s some good news. Once the Chinese government and people realized what was happening, and took the proper measures, the rate of infection dropped considerably and the situation is now under control. Travel restrictions, social isolation, and city-wide lockdowns made all the difference.

“Heightened awareness of the outbreak, increased use of personal protective measures, and travel restriction have helped reduce the overall force of infection; however, it is unclear whether this reduction will be sufficient to fully stem the virus spread,” Shaman concludes. “If the novel coronavirus follows the pattern of 2009 H1N1 pandemic influenza, it will also spread globally and become a fifth endemic coronavirus within the human population.” 

Travel restrictions, closed borders, locked down cities — these are words and phrases usually reserved for works of fiction, but this is the reality of the situation. These are major inconveniences, no doubt, but they’ll be worth it once we’ve beaten this unwelcome viral intruder. 

The full study can be found here, published in Science.