Does Delta Increase Hospitalizations in Adults?

Investigators analyzed data from COVID-NET across 14 states as this variant quickly become the dominant strain within the United States.

Currently in the United States, there is a 7-day daily average of 5,075 hospitalizations. Since the SARS-CoV-2/COVID-19 pandemic began, over 3.2 million hospitalizations have occurred in the United States due to the disease. More recently there were over 81,000 new cases reported on November 9 with a 7-day daily average of nearly 75,000. As the US, like so many countries, has struggled with response to COVID-19, the more transmissible variant, Delta, has furthered stressed efforts.

Since the identification of the Delta variant (B.1.617.2), questions have also arisen regarding its impact on hospitalizations and severity of disease. A new study published within the Center for Disease Control and Prevention (CDC)’s Morbidity and Mortality Weekly Report (MMWR) regarding this very issue. Seeking to address unknowns about Delta and disease severity in adults, the research team analyzed data from COVID-NET across 14 states as this new variant had quickly become the dominant strain within the United States.

COVID-NET was a resource designed by the CDC which studied hospitalization trends for the disease across the United States. From this database, the team assessed trends in those aged 18 years or older, hospitalized for COVID-19 during periods before Delta became the predominant strain (January to June 2021) and during its predominance (July to August).

The research team found that in those non-pregnant hospitalized adults, there was not a significant change between pre-Delta and Delta periods in those admitted to intensive care units (ICUs), receiving mechanical ventilation, or died. The authors noted that, “The proportion of hospitalized COVID-19 patients who were aged 18–49 years significantly increased, from 24.7% (95% confidence interval [CI] = 23.2%–26.3%) of all hospitalizations in the pre-Delta period, to 35.8% (95% CI = 32.1%–39.5%, p<0.01) during the Delta period. When examined by vaccination status, 71.8% of COVID-19–associated hospitalizations in the Delta period were in unvaccinated adults. Adults aged 18–49 years accounted for 43.6% (95% CI = 39.1%–48.2%) of all hospitalizations among unvaccinated adults during the Delta period. No difference was observed in ICU admission, receipt of IMV, or in-hospital death among nonpregnant hospitalized adults between the pre-Delta and Delta periods. However, the proportion of unvaccinated adults aged 18–49 years hospitalized with COVID-19 has increased as the Delta variant has become more predominant. Lower vaccination coverage in this age group likely contributed to the increase in hospitalized patients during the Delta period.”

This analysis of over 87,000 hospitalizations over this period of time shed light on the rates as Delta began to take hold within the United States. The authors also noted several interesting findings, including 71.8% of hospitalized patients in a sample of 7615 were not vaccinated. Among those unvaccinated hospitalized COVID-19 patients, “the average monthly proportion who were aged 18–49 years significantly increased from 26.9% in the pre-Delta period to 43.6% during the Delta period (p<0.01)”.

Ultimately, this study reinforces the importance of vaccination but also that while more transmissible, the Delta variant does not appear to increase hospitalizations for adults.