this report was posted as an MMWR Early Release on the MMWR website (https://www.cdc.gov/mmwr).In mid-June 2021, B.1.671.2 (Delta) became the predominant variant of SARS-CoV-2, the virus that causes COVID-19, circulating in the United States. As of July 2021, the Delta variant was responsible for nearly all new SARS-CoV-2 infections in the United States.* The Delta variant is more transmissible than previously circulating SARS-CoV-2 variants (1); however, whether it causes more severe disease in adults has been uncertain. Data from the CDC COVID-19-Associated Hospitalization Surveillance Network (COVID-NET), a population-based surveillance system for COVID-19-associated hospitalizations, were used to examine trends in severe outcomes in adults aged ≥18 years hospitalized with laboratory-confirmed COVID-19 during periods before (January-June 2021) and during (July-August 2021) Delta variant predominance. COVID-19-associated hospitalization rates among all adults declined during January-June 2021 (pre-Delta period), before increasing during July-August 2021 (Delta period). Among sampled nonpregnant hospitalized COVID-19 patients with completed medical record abstraction and a discharge disposition during the pre-Delta period, the proportion of patients who were admitted to an intensive care unit (ICU), received invasive mechanical ventilation (IMV), or died while hospitalized did not significantly change from the pre-Delta period to the Delta period. 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.

The temperature distribution T(x), maximum temperature difference ΔTmax, and coefficient of performance ε are determined for an Ettingshausen cooler of rectangular cross section when the temperature is constant in the direction of current flow (longitudinal isothermal condition). The calculation is carried out for the two cases (1) temperature-independent transport coefficients and (2) the Nernst and resistivity coefficients proportional to T−1. In both cases the expressions for ΔTmax and ε correspond closely to those for the transversely isothermal Peltier cooler while the temperature distribution differs considerably. In the longitudinally isothermal Ettingshausen cooler the electric field is constant, in the contrast to the transversely isothermal Peltier cooler, in which the current density is constant. Recognition of this fact allows the validity of the results to be established for all possible values of the figure of merit. A value of ΔTmax measured on a Bi(97)Sb(3) cooler is compared with the value determined by substitution of independently measured values of the transport coefficients into the theoretical expression for ΔTmax. Although the temperature dependence of the transport coefficients is not taken into account exactly, the agreement is good. The effect of shaping the cooler (in effect, cascading) is discussed and experimental evidence for enhancement of cooler performance due to shaping is presented.

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A thermal radiation detector based on the Nernst effect is capable of relatively high-speed operation without loss of responsivity or detectivity (D*) over its low-frequency values. The effective decoupling of the responsivity and thermal time constant is the result of the specific characteristics of the Nernst effect. Results are presented for materials having optimum properties for operation at room temperature (Bi), as well as lower temperatures (Bi97Sb3).