Since the early days of the epidemic, researchers have found that people with COVID-19 can spread the disease before they develop symptoms and even if they never feel ill.
A study published in Journal of the American Medical Association On Thursday, how many new cases are transmitted to people without symptoms: at least 50 percent.
The findings echo what the Centers for Disease Control and Prevention provided in November, when the agency said people with no symptoms were “estimated to transmit more than 50 percent.”
Jesse Butler, deputy director for infectious diseases at the CDC and lead author of the new study, said the findings reinforce the importance of adhering to public-health guidelines about wearing and removing masks.
“There was still some controversy over the value of community facing, face masks, social distancing, and hand hygiene,” Butler told Business Insider. “This study demonstrates that while symptom screening can have significant value, mitigation, as well as significant planned benefit testing of individuals in certain settings.”
For the study, researchers modeled potential COVID-19 transmitters in three groups: pre-symptomatic (people who did not yet have symptoms), never symptomatic and symptomatic.
The researchers then created the model that each group would transmit COVID-19, the day people were most infectious. At baseline, they assumed that people of all groups would be most infected five days after exposure to coronovirus. This is what researchers have found for medieval incubation periods – most people take the time to develop symptoms after exposure.
The model initially assumed that 30 percent of people were asymptomatic, and that 75 percent of those people were contagious or eventually showing symptoms. Based on those assumptions, the results suggested that asymptomatic people alone were responsible for 24 percent of infections.
But the researchers also modeled scenarios in which peak infectivity occurred after three, four, six, and seven days, and they increased and decreased the percentage of asymptomatic people in the model, as well as their infectious rates relative to other groups.
In most of these scenarios, at least 50 percent of new infections were found in people with no symptoms (asymptomatic and prismoptomatic).
“The ratio of transmissions to a wide range of base values generally remained above 50 percent,” Butler said, adding that the consistency of that finding was surprising.
Even in the most conservative estimate, in which peak infectiousness occurred seven days after exposure and asymptomatic people accounted for 0 percent of transmission, the pre-symptomatic group still accounted for more than 25 percent of cases overall, according to the model. Caused
Butler and his colleagues cautioned, however, that their model likely underestimated the actual percentage of COVID-19 cases driven by people without symptoms, as they calculated transmission rates if everyone were to rotate at random. But in fact, many restaurants and other establishments screen for fever and other symptoms that prevent symptomatic people from entering. Additionally, many people with symptoms are isolated at home, which makes them less likely to spread COVID-19 than those who feel healthy.
This article was originally published by Business Insider.
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