Adults aged 20 to 49 may have generated 72.2% of the resurgences of COVID-19 in the US from late summer 2020, with those aged 35 to 49 contributing especially, a study published yesterday in Science suggests.
A team led by researchers at Imperial College London analyzed age-specific mobile phone mobility data for more than 10 million Americans and linked it to age-specific COVID-19 mortality data as of March 15, 2020.
Data from 42 US states, Washington, DC and New York showed that the number of visits to places like supermarkets and restaurants started to recover in all age groups in August, after a significant initial reduction due to public health interventions, such as locks in the spring. COVID-19 infections and deaths followed a similar pattern in the United States and Europe.
Among all the locations evaluated, up to mid-August, it was estimated that the age group 35 to 49 years old contributed to 41.1% of the transmission of the virus, compared with 2.1% in the age group 0-9 years, 4.0% in those aged 10 to 19, 34.7% in those aged 20 to 34, 15.3% in those aged 50 to 64 years, 2.5% in those aged 65 to 79 years and 0.3% in those aged 80 years or more. The number of deaths from coronavirus did not increase significantly after schools reopened in the fall.
The proportion of different age groups among deaths from COVID-19 has remained relatively constant over time, in contrast to the large changes in their relative proportion of cases.
“Based on the combined data on mobility and mortality, we found that the reconstructed fluctuations in age-specific reproduction numbers had only a relatively modest impact on the age groups’ contribution to progressive spread over time, and no evidence that young adults 20-34 years old were the main source of the resurgence of COVID-19 in the United States during the summer of 2020 “, wrote the authors.
But in October 2020, the 20-49 age group was the only one with a reproduction number – or number of secondary people infected per case – above 1, which is the level required for an outbreak to expand. The estimated contribution for distribution by age groups at that time was 72.2% for adults aged 20 to 49, against less than 5% for children aged 0 to 9 and less than 10% for adolescents aged 10 to 19.
Targeted interventions to contain the spread, deaths
Over time, COVID-19 transmission rates have varied widely in the United States, with higher rates attributed to the 20-49 age group and those aged 20-34 in the south, southwest and west regions of the country.
“We found that adults aged 20 to 49 are the main drivers of the COVID-19 epidemic in the United States and are the only age groups that contribute disproportionately to the spread, in relation to population size,” said lead author Melodie Monod, MSc, in a press release from Imperial College London. “Although children and adolescents have contributed more to the spread of COVID19 since school closure mandates were suspended in the fall of 2020, we found that this dynamic has not changed substantially since the schools reopened.”
The authors called for targeted interventions, such as vaccines to reduce transmission to people aged 20 to 49, as a strategy to reduce the likelihood of future outbreaks of COVID-19 and related deaths in areas not yet affected by new highly transmissible coronavirus variants. “Adults aged 20 to 49 naturally have more contacts with other adults aged 20 and older,” wrote the authors in the study, adding that the age group is more vulnerable to the virus and more mobile than younger people.