From the earliest days of the pandemic, researchers know that people with COVID-19 can spread the disease before they develop symptoms and even if they never feel sick.
A study published in Journal of the American Medical Association on Thursday it quantifies how many new cases are transmitted from asymptomatic people: at least 50%.
The findings echo estimates provided by the Centers for Disease Control and Prevention in November, when the agency said “asymptomatic people are estimated to account for more than 50 percent of transmissions.”
Jay Butler, CDC deputy director of infectious diseases and lead author of the new study, said the findings reinforce the importance of following public health guidelines on the use and distancing of masks.
“There was still some controversy over the value of community mitigation (facial masks, social distancing, and hand hygiene) to limit the spread,” Butler told Business Insider. “This study shows that while symptom screening may have some value, mitigation, as well as strategically planned testing of people in some setting, will be a major benefit.”
For the study, the researchers modeled potential COVID-19 transmitters into three groups: pre-symptomatic (people who had not yet had symptoms), never symptomatic, and symptomatic.
The researchers modeled how much each COVID-19 group would transmit based on the day people were most infectious. At first, they assumed that people in all groups would be more infectious five days after being exposed to the coronavirus. This is what researchers have discovered as the average incubation period: the time it takes most people to develop symptoms after exposure.
The model initially assumed that 30% of people were asymptomatic and that those people had 75% infection like people who had symptoms. Based on these assumptions, the results suggested that only asymptomatic people were responsible for 24 percent of infections.
But the researchers also modeled scenarios in which maximum infectivity occurred after three, four, six, and seven days, and increased and decreased the percentage of asymptomatic people in the model, as well as their rate of infectivity over others. groups.
In most of these scenarios, asymptomatic people (asymptomatic and presymptomatic) were found to transmit at least 50% of new infections.
“The proportion of transmissions was generally kept above 50 percent across a wide range of core values,” Butler said, adding that the consistency of this finding was striking.
Even in the most conservative estimate, in which maximum infectivity occurred seven days after exposure and asymptomatic individuals accounted for 0 percent of transmission, the presymptomatic group still caused more than 25 percent. of cases in general, depending on the model.
Butler and his co-authors warned, however, that their model probably underestimates the actual percentage of COVID-19 cases driven by asymptomatic people, as they calculated transmission rates if everyone moved at random. But in reality, many restaurants and other establishments detect fevers and other symptoms to prevent the entry of symptomatic people. In addition, many people with symptoms are isolated at home, which also makes them less likely to contract COVID-19 than people who feel healthy.
This article was originally published by Business Insider.
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