‘Silent Spreaders’ Possibly Key to Rapid Spread of COVID-19 According to Yale University led Study

‘Silent Spreaders’ Possibly Key to Rapid Spread of COVID-19 According to Yale University led Study

A Yale University study led by epidemiologist Alison Galvani reports that so-called silent spreaders may be responsible for up to half of the COVID-19 infections in the United States. Unlike some other viruses such as Ebola, Galvani reports to NPR’s Lulu Garcia-Navarro that with COVID-19 the most contagious period Is before the infected are even sick. That is, the “peak of contagiousness” occurs during the “presymptomatic” phase of the illness. This spells trouble for Americans, and anyone else, that wants to just get out, be near other people and enjoy the summer or even go to work. How about opening up the schools in mid to late August? Not so fast, answers this study’s co-author. As this understandably natural impulse (that is to get outside and be with others) led to pent up outdoor activities during Memorial Day, America is now paying the price with record SARS-CoV-2 surges across big swathes of the country. But the economic toll of further lockdown and quarantines spells real trouble as the social misery index is certain to rise.

The Study

The study highlights the importance of understanding presymptomatic and asymptomatic transmission of COVID-19. Based on an analysis of recent individual-level data regarding infectiousness before symptom onset and the asymptomatic percentage of all infections, the Yale-led team found that the majority of incidences is probably attributable to so called “silent transmission” arising out of a combination of the presymptomatic stage and asymptomatic infections, Dr. Galvani explains to the NPR host.


The study unfortunately offers more bad news. Based on the Yale model even if all COVID-19 infected persons with symptoms were isolated, sizeable and tragic outbreaks of the disease would more than likely continue because a great deal of this disease is spreads via the silent transmission, that is by those that have been infected by COVID-19 but yet have no symptoms, which is typically the first five days from onset of infection. More specifically, the last two days during this silent period is the most contagious, hence the fourth and fifth days post infection. Yet these people are almost always presymptomatic—they look perfectly healthy.

The research team ran models to account for isolation of those that were presymptomatic and found that over one-third (33%) of silent infections must be isolated to actually suppress a future outbreak below 1% of the population or about 3 million in America.

Take Away

Federal and state government leaders must understand that if they seek to curtail this ongoing crisis they must supplement symptom-based isolation with rapid contact tracing and rapid and effective testing that identifies asymptomatic and presymptomatic cases before current restrictions can be lifted, including the opening of schools according to Ms. Galvani. Put another way, this means that the well-intentioned urge to further open up the society, including schools in just over a month, could just put “oil on the fire.”

Lead Research/Investigator

Alison Galvani, PhD, Burnett and Stender Families Professor of Epidemiology (Microbial Diseases); Director of the Center for Infectious Disease Modeling and Analysis (CIDMA)

Other research authors can be seen here

Call to Action: The implications here are tricky. With enormous economic and social pressure to further open life up countervailing scientific observation raises caution with moving too fast, and in fact, suggests not enough is done yet in regards to granular testing and contact tracing. In an election year, vast amounts of power, prestige and money, not to mention ideological direction, from tax policy to health care, are at stake and any rational and common sense discussions may get hijacked by further politicization, which only punishes most of the people. Pressure for greater investments in testing and advanced forms of contact tracing that can integrate into American culture merit highest order of attention should this Yale analysis be correct.  In the meantime, the pandemic’s economic consequences will snowball as many of the temporary social supports put in place will soon dissipate. Already a great number of evictions are reported in cities such as New Orleans. Social problems may escalate as we progress into the late summer and into the fall leading to a new set of unfolding crisis dynamics to deal with.