Filenews 27 August 2021
Despite the fact that the coronavirus is already more than 1.5 years our "companion", scientists are still struggling to understand when exactly and to what extent infected people are most likely to transmit it to those around them.
A new study done by Boston university's School of Public Health claims that people infected with SARS-CoV-2 are more infectious two days before and three days after the onset of symptoms.
As stated in a related article by JAMA Internal Medicine, the researchers observed that carriers of the coronavirus were more likely to be asymptomatic if they had contracted the virus from a person who was also asymptomatic.
"In previous studies we have seen that viral load can be an indirect way of measuring infectivity," says Dr. Leonardo Martinez, associate professor of Epidemiology at the American University, who together with Dr. Yang Ge, a researcher from the department of Epidemiology and Biostatistics at the University of Georgia's College of Public Health, did this study.
"So we wanted to see if it is confirmed that COVID-19 is more contagious some days before and after the onset of symptoms," he adds.
Dr. Martinez studied the transmission of COVID-19 infection in a sample of nearly 9,000 close-contact cases in China's Zhejiang province between January 2020 and August 2020. "Close contacts" included people living in the same house or dining together, co-workers, people in hospital settings, and those who shared the same transport vehicle. Experts had placed infected people under medical supervision for at least 90 days after the initial positive coronavirus test so that they could distinguish between asymptomatic and pre-symptomatic cases.
Of the people who had been classified as an "initial case", 89% developed mild or moderate symptoms and only 11% were asymptomatic, while no one developed a serious disease. Family members of the initial cases, who had been exposed multiple times or for a long time to the carrier had a higher rate of infectivity than other close contacts. But regardless of this risk factor, they were more likely to catch the coronavirus than the initial case if they had been in contact with it just before or after the point in time when the initial case manifested noticeable symptoms.
Compared to people who had mild and moderate symptoms, asymptomatic initial cases were less likely to transmit the coronavirus to their close contacts, while the latter were also less likely to have noticeable symptoms.
"The study comes to validate the necessity of vaccination, which reduces the clinical severity of COVID-19 among those who eventually become ill," concludes Dr. Leonardo Martinez.
