Researchers now believe that at least 50% of new coronavirus cases stem from asymptomatic carriers based on study findings by researchers with the Centers for Disease Control and Prevention.

An analysis published Thursday in JAMA found that 59% of all disease transmission came from asymptomatic individuals — with 35% of those being presymptomatic people and 24% people who never developed symptoms. 

Researchers believe that it’s a plausible scenario that at least 50% of disease spread can be linked to people who didn’t have symptoms at all based on the analysis. The findings also suggest that simply finding and isolating symptomatic COVID-19 patients alone will not help control and stop the spread of the disease, noted researchers Michael A. Johansson, Ph.D., Talia M. Quandelacy, Ph.D., Sarah Kada, Ph.D., et al. 

The findings bolster support for providers who may have unknowingly spread the virus among long-term care facilities, especially during the very first days of outbreaks in the U.S. Operators have been pilloried in some sectors of the public discourse because so many have workers who circulate among more than one building, unknowingly becoming powerful transmission vectors for COVID-19.

The research supports a November study that called on nursing homes to consider testing their workers more frequently than what federal standards dictate after the analysis revealed that method may not catch all asymptomatic workers.

The Centers for Medicare & Medicaid Services in September announced mandatory coronavirus testing of nursing home staff would be based on county-level data. 

Counties with low or fairly low positivity rates are designated as green or yellow, while those with higher rates are red counties. Nursing homes in green counties have to test staff once per month; yellow counties must test staff once per week; and staff in red counties must be tested twice per week. 

“This strategy may miss over half of the facilities with a SARS-CoV-2 infected staff member, particularly if asymptomatic,” they wrote at the time.