The CDC model found that people without symptoms spread the virus in more than half of cases

Fifty-nine percent of all transmissions came from people without symptoms, according to the model’s baseline scenario. This includes 35 percent of new cases from people who infected others before they developed symptoms and 24 percent of people who had no symptoms at all.

“The whole point is to control the Covid-19 pandemic. It will really require controlling the silent epidemic of transmission of infection from people without symptoms,” he said. Jay C. Butler, Deputy Director of the CDC for Infectious Diseases and co-author of the study. “Community-based mitigation tools that we need to use on a large scale to be able to slow the spread of SARS-CoV-2 from all infected people, at least until these vaccines are widely available.”

The appearance of a A more contagious variant, Which was first discovered in the UK and has since been found in several US states, the importance of these guidelines receives in a more apparent dilution. “These results are in bold, italic, and underlined,” Butler said. “We have moved from the 11 point line to the 16 point line.”

The epidemiologist said: “It’s definitely a confirmation, but it’s good to see confirmation.” Richard Menzies, Who runs the McGill International TB Center in Canada and was not involved in this research. “These are powerful and believable results.”

Many factors influence how the Coronavirus spreads. The researchers took a recognized, uncomplicated approach – Butler called it a “fairly simple mathematical model” – and used this to evaluate several scenarios, changing the infectious period and the rate of transmission of people who had no symptoms at all.

The model consistently predicted that asymptomatic spread accounted for roughly half of the virus transmission. “I was a little surprised at how long it persisted under a wide range of underlying assumptions,” said Butler, such as changing the timing of the infection peak from four days after infection to five or six days.

But Moog CivicAn infectious disease expert at the University of St Andrews in Scotland has argued that some of the model’s assumptions are flawed. Civic said the best estimate of the relative infection of people without symptoms versus those with them was 35 percent, derived from Scientific literature review Posted in September.

Instead, the study authors estimated that, at baseline, people without symptoms were 75 percent contagious. Butler said the number came from an analysis of their literature including peer-reviewed research and prepress research. “I have no doubt that we still have someone say, ‘Well, what if I did such-and-such-y or z-do? “But we hope that being able to adjust variables helps address some of those concerns, like what we did.

Cevik also noted that the study does not take into account the environment in which diffusion occurs. “Asymptomatic transmission may be important, but it may be more important in long-term care facilities and families,” she said. “It could mean that we need to do more targeted testing for high-risk populations,” rather than a blanket screening.

It is not yet certain whether vaccines stop transmission of the coronavirus or not, and a scenario has not been addressed in this model. “The data on the effect of vaccines on asymptomatic infection is very limited,” Butler said, although he expected more information in the coming months.

Clinical trials of mRNA vaccines, which were authorized in December, concluded that the vaccines are High capacity To prevent symptomatic disease. But those experiments did not determine whether the vaccinated people were able to spread the pathogen.

Menzies warned that “if symptoms are asymptomatic but equally contagious, this will have a major impact on the epidemic.” That is why it is so important to continue testing people, especially those who have been vaccinated and then exposed to the virus, he said.