A new study has identified adults aged 20 to 49 as the biggest spreaders of COVID-19 in the U.S. - accounting for 75% of all spreaders.
The study published in the journal Science estimated people aged 35 to 49 accounted for 41% of new transmissions through mid-August while those aged 20 to 34 years were responsible for another 35%.
Children and teens accounted for 6% of spreaders. People 50 to 64 made up 15% of transmission.
These adults accounted for an estimated 72.2% of infections in the U.S. locations included in the study after schools reopened in October.
"We find adults aged 20 to 49 are a main driver of the COVID-19 epidemic in the U.S. and are the only age groups contributing disproportionally to onward spread, relative to their population size," said Dr. Melodie Monod of the Imperial College COVID-19 Response Team.
"While children and teens contribute more to COVID-19 spread since school closure mandates have been lifted in fall 2020 we find these dynamics have not changed substantially since school reopening," she noted.
Adults aged 35 to 49 are the biggest factor driving the pandemic when compared with younger adults, affirms Dr. Oliver Ratmann, also of the Imperial College COVID-19 Response Team.
"This study provides evidence that the resurgent COVID-19 epidemics in the U.S. in 2020 have been driven by adults aged 20-49, and in particular adults aged 35-49, before and after school reopening," according to the study.
"Before the implementation of COVID-19 interventions, contacts concentrated among individuals of similar age, were highest among school-aged children and teens, and also common between children/teens and their parents, and middle-aged adults and the elderly," noted the study.
"Since the beginning of the pandemic, these contact patterns have changed substantially."
The study indicates that in locations where virus lineages have not been established, additional interventions among adults aged 20 to 49 might bring COVID-19 outbreaks under control and avert deaths.
These interventions include mass vaccination campaigns such as those being carried out in the United States since late December 2020. The study argues vaccinations should probably focus on those aged 20 to 49.
Vaccination guidance from the U.S. Centers for Disease Control and Prevention, however, prioritizes front-line health care workers and frail long-term care facility residents.
The study reveals that over time, the share of age groups among reported deaths has been quite constant. This finding suggests young adults are unlikely to be the primary source of resurgent epidemics, or infection waves, since the summer 2020.
Instead, it's "the changes in mobility and behavior among the broader group of adults aged 20-49 underlie resurgent COVID-19 in the U.S. in 2020," according to the study.
