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Studies Question Asymptomatic Transmission of COVID-19

Two papers in leading medical journals have raised questions about the frequency of transmission of the SARS-CoV-2 virus from people showing no symptoms of the disease.

The results are noteworthy because many COVID-19 mitigation strategies are based on the presumption of asymptomatic spread. The issue first gained prominence in June when a World Health Organization official said spread with no symptoms is “very rare.” The official, Maria Van Kerkhove, walked back her comment after public health experts complained.

Contacts Didn’t Get Sick

On December 14, JAMA Network Open published an article documenting a meta-analysis of 77,758 participants in 54 studies. Within those studies, researchers were able to review transmission of household members with no symptoms and in some cases, showed symptoms later.  The infection rate by those individuals was  0.7 percent.

When an individual showed symptoms, the spread was 18 percent. The authors stated “these findings are consistent with other household studies reporting asymptomatic index cases as having a limited role in household transmission.”

A study published in Nature Communications on November 20 showed similar results. The authors looked at 300 asymptomatic people in Wuhan from May 4 to June 1 who tested positive on PCR tests.

In fact, 190 of the 300 individuals showed antibodies to COVID-19, indicating they had recovered from past exposure. The researchers then identified 1,174 contacts of the 300 individuals and found none tested positive for COVID-19.

“Compared with symptomatic patients, asymptomatic infected persons generally have a low quantity of viral loads and a short duration of viral shedding, which decrease the transmission risk of SARS-CoV-2,” the authors state.

Instead of looking at the results from the perspective of transmission, the public should look at it from the view of the exposed, says John Goodman, president of the Goodman Institute and co-publisher of Health Care News. “This is consistent with the judgment that 80 percent of the population is immune. It is similar to the infection rate among sailors living in close quarters on the aircraft carrier and on the cruise ship, reported last spring,” said Goodman.

The reference is to early outbreaks of COVID-19 aboard the USS Theodore Roosevelt and the cruise ship, the Diamond Princess, in which a number of passengers did not get sick.


AnneMarie Schieber (amschieber@heartland.org) is managing editor of Health Care News.


Internet Info:

Zachary Madewell, Ph.D., Yang Yang, Ph.D., Ira Longini, Ph.D., “Household Transmission of SARS-CoV-2—A Systematic Review and Meta-analysis,” JAMA Network Open, December 14, 2020: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2774102


Shiyi Cao et. al., “Post-lockdown SARS-CoV-2 Nucleic Acid Screening in Nearly Ten Million Residents of Wuhan, China,” Nature Communications, November 20, 2020: https://www.nature.com/articles/s41467-020-19802-w

AnneMarie Schieber
AnneMarie Schieber is a research fellow at The Heartland Institute and managing editor of Health Care News, Heartland's monthly newspaper for health care reform.


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