Background: The δ (delta) variant has spread rapidly worldwide and has become the predominant strain of SARS-CoV-2. We analyzed an outbreak caused by a vaccine breakthrough infection in a hospital with an active infection control program where 91.9% of healthcare workers were vaccinated. Methods: We investigated a SARS-CoV-2 outbreak between September 9 and October 2, 2021, in a referral teaching hospital in Korea. We retrospectively collected data on demographics, vaccination history, transmission, and clinical features of confirmed COVID-19 in patients, healthcare workers, and caregivers. Results: During the outbreak, 94 individuals tested positive for SARS-CoV-2 using reverse transcription-polymerase chain reaction (rtPCR) testing. Testing identified infections in 61 health care workers, 18 patients, and 15 caregivers, and 70 (74.5%) of 94 cases were vaccine breakthrough infections. We detected 3 superspreading events: in the hospital staff cafeteria and offices (n = 47 cases, 50%), the 8th floor of the main building (n = 22 cases, 23.4%), and the 7th floor in the maternal and child healthcare center (n = 12 cases, 12.8%). These superspreading events accounted for 81 (86.2%) of 94 transmissions (Fig. 1, 2). The median interval between completion of vaccination and COVID-19 infection was 117 days (range, 18–187). There was no significant difference in the mean Ct value of the RdRp/ORF1ab gene between fully vaccinated individuals (mean 20.87, SD±6.28) and unvaccinated individuals (mean 19.94, SD±5.37, P = .52) at the time of diagnosis. Among healthcare workers and caregivers, only 1 required oxygen supplementation. In contrast, among 18 patients, there were 4 fatal cases (22.2%), 3 of whom were unvaccinated (Table 1). Conclusions: Superspreading infection among fully vaccinated individuals occurred in an acute-care hospital while the δ (delta) variant was dominant. Given the potential for severe complications, as this outbreak demonstrated, preventive measures including adequate ventilation should be emphasized to minimize transmission in hospitals.

Funding: None

Disclosures: None

The swelling behavior of chitosan hydrogels in ionic liquid–water binary systems was studied using hydrophilic room-temperature ionic liquids (RTILs) to elucidate the swelling properties of chitosan hydrogels. It was confirmed that chitosan hydrogels are much stiffer after immersing in a pure RTIL because the water existing inside the chitosan polymer network is extracted into the RTIL. The pH of the binary system changes when the RTIL is in contact with water. The chitosan hydrogels were fully dissociated at a 90% water content in the BMI-BF4-water binary system. The equilibrium binary system content behavior of the chitosan hydrogels depended upon the amount of free water present. The water behavior in a pure RTIL was examined using differential scanning calorimetry.

Composite fibers composed of chitosan and single-wall carbon nanotubes (CNTs) have been fabricated using a wet spinning method. The dispersion was improved by the sonic agitation of the CNTs in a chitosan solution followed by centrifugation to remove tube aggregates and any residual catalyst. The mechanical behavior was investigated using a dynamic mechanical analyzer (DMA). The mechanical tests showed a dramatic increase in Young's modulus for the chitosan/CNT composite fibers fabricated using the improved dispersion method. The strain on the microfibers was determined from tensile load measurements during pH switching in acidic or basic electrolyte solutions. The microfibers showed a general actuation behavior of expanding at pH = 2 and contracting at pH = 7 under low tensile loads. However, a reverse of this actuation behavior was exhibited under high tensile loads. This anomalous pH actuation is both new and surprising. It was explained from an analysis of the differences in sample stiffness and Poisson’s ratio under tensile load in electrolyte solutions with different pH values.

Composite nanofibers including ferritin nanoparticles or multiwalled carbon nanotubes (MWCNTs) were fabricated to enhance the physical properties of the nanofibers, such as the elastic modulus and electrical conductivity. The ferritin was homogeneously incorporated in the polymeric nanofibers, but excess carbon nanotubes (CNTs) added to the polymer solution resulted in the fabrication of composite nanofibers with rough surfaces. PVA/ferritin/CNT composite nanofibers were fabricated that had smooth surfaces, and had a good dispersion of ferritin and CNTs. These composite nanofibers are applicable to artificial muscles requiring enhanced physical properties.

Ferroelectric BaTiO 3 thin films with perovskite structure were grown by sol-gel spin-on processing onto (111)Pt/Ti/SiO2/Si substrates. In order to investigate the effects of space charge in BaTiO3 thin films, we measured the relative dielectric constant and the ac conductivity of the films as a function of frequency, ac oscillation amplitude and temperature. Dielectric constant and dielectric loss were 147 and 0.03 at 100 kHz, respectively. Also, BaTiO3 thin films exhibited marked dielectric relaxation above the Curie temperature and in the low frequency region below 100 Hz. This low frequency dielectric relaxation is attributed to the ionized space charge carriers such as oxygen vacancies and defects in BaTiO3 film and the interfaical polarization. The thermal activation energy for the relaxation process of the ionized space charge carriers was 0.72 eV.

Basic mechanisms for both Ni- and Pd-metal induced lateral crystallization (MILC) are investigated. For both cases, tiny silicides were formed under the metal deposited area, and propagated toward amorphous Si films leaving crystallized Si behind at temperatures as low as 500 °C. Ni-MILC was influenced by Pd such that the lateral crystallization rate was enhanced, and the temperature for the lateral crystallization was lowered to 450 °C. Through TEM analysis and external stress experiments, it was found that the enhancement of the lateral crystallization rate was closely related to the compressive stress generated by the formation of nearby Pd2Si.