Younger adults drove COVID-19 resurgence in US, study finds
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People aged 20 to 49 years were “the only age groups” sustaining the COVID-19 resurgence last fall in the United States, according to a study published in Science.
“We were intrigued by early studies indicating that children were substantially less likely to get infected with COVID-19 than adults, which is atypical for respiratory infectious diseases,” Alexandra Blenkinsop, PhD, a postdoctoral researcher at the Amsterdam Institute for Global Health and Development, told Healio.
“We then reviewed studies from earlier coronaviruses SARS in particular suggesting that school closures had near zero positive effect in delaying or mitigating SARS outbreaks,” Blenkinsop said. “This led us to speculate that COVID-19 spread differs from how other respiratory infectious diseases spread in terms of age groups.”
Blenkinsop and colleagues used detailed, longitudinal and age-specific population mobility and COVID-19 mortality data to estimate how non-pharmaceutical interventions — as well as changing contact intensities, age and other factors — affected the resurgence of COVID-19.
According to Blenkinsop, the study demonstrated that more than 65% of COVID-19 infections originated from individuals aged 20 to 49 years despite them accounting for only 40% of the population on average. Additionally, the researchers found that the proportion of new infections from those aged 35 to 49 years were the highest drivers, an effect that was similar across states, though infections from those aged 20 to 34 years were found to be higher in Southern and Western states compared with the rest of the U.S.
According to Blenkinsop, the researchers estimated that people in the 20- to 49-year-old age group were the only individuals that consistently had reproduction numbers greater than 1 an effect that was consistent over time, including after school reopenings in the fall, and consistent geographically.
“We have seen in many countries that non-pharmaceutical interventions and correct mask-wearing have been effective in reducing the spread of new infections,” Blenkinsop said, adding that targeting these high-spread age groups with measures that help adults cover daily household expenses, such as ensuring continued unemployment benefits, could help working adults stay at home when they need to and lessen spread.
“With the evidence we provide, it does not seem justifiable to open non-essential services, such as restaurants or bars, while school closures are mandated or encouraged,” Blenkinsop said.
She added that once older, at-risk populations are vaccinated, spread could be “substantially mitigated” if adults aged 20 to 49 years are then vaccinated provided vaccines are proven to block transmission sufficiently.
“Even with the rollout of vaccination programs, there is an important need to maintain measures to restrict contacts, and therefore transmissions, from 20- to 49-year-olds,” Blenkinsop said. “When there are resources available, vaccination of these groups will also be effective in reducing infection burden.”
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