Shortly after SARS-CoV emerged at the turn of the 21st century, the spike (S) protein (particularly in its prefusion [native] conformation) was identified as the immunodominant antigen of the virus. 1 Evaluation of patients with SARS-CoV-2 revealed that binding and neutralizing antibodies primarily target the receptor-binding domain of the S1 subunit. 2 Once this putative vaccine target was identified, the next challenge was how to best generate an effective immune response to SARS-CoV-2. The characteristics of this response would include production of neutralizing antibodies, generation of a T-cell response, and avoidance of immune-enhanced disease (vaccine-induced response that led to paradoxically increased disease severity on viral challenge). 3 Several vaccine designs were evaluated by different groups during the development of a SARS-CoV-2 vaccine. The SARS-CoV-2 vaccines currently authorized for use, and others that have late-stage clinical data available, are summarized in the Table.

Films of chitosan, prepared by different fabrication processes, were examined at several structural levels, from the molecular to the macroscopic. This revealed the presence of polymorphic crystal forms, which varied with film treatment. Similarly, morphological structures varying from spherulites to rods were formed, depending on film processing conditions. The effect of structure on the mechanical properties, as well as the orientability of the films, were also investigated.

SynopsisThe melting behavior of restrained isotactic polypropylene fibers is examined quantitatively in terms of the influence the anisotropic structural state of the polymer has on the observed properties. Two endotherm peaks are observed to occur in some of the samples. The formation and location of the multiple peaks are determined by the orientation of the noncrystalline chains, and is independent of the fabrication path used to achieve that orientation. Above a certain minimum orientation of the noncrystalline chains, multiple endotherm peak formation occurs. The high-temperature endotherm ( 2 ' 2~) extrapolates to an ultimate melting point for fully oriented noncrystalline chains of 22OoC, while the lower-temperature endotherm (TIM) extrapolates to an ultimate melting point of 185OC. Noncrystalline chain orientation influences the endotherm temperature through its changing cox$guational entropy. It is shown quantitatively that the noncrystalline polymer must be considered as plastically deformed, since rubber elasticity theory is not followed as predicted. The melting behavior of isothermally crystallized samples are also reported to further elucidate the nature of the observed endotherms.

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synopsisThe submicroscopic morphology of uniaxially deformed isotactic polypropylene films has been examined by x-ray diffraction, infrared dichroism, birefringence, sonic modulus, small-angle light scattering, density, and electron microscopic techniques. Several new theoretical relationships and techniques have been developed. These include (I) a twophase sonic modulus theory which makes possible the determination of the amorphous orientation function and the intrinsic sonic moduli of the polymer, (8) a general relationship for the quantitative determination of the infrared transition moment angle and for the quantitative determination of the crystal orientation function from infrared dichroism measurements only, (3) the determination of the extension ratio of spherulites from the small-angle light-scattering patterns of deformed films, (4) a technique for the experimental dete&mation of the intrinsic birefringence of the crystal and amorphous regions of isotactic polypropylene, (6) correlation of the polarisability difference determined from solid-state measurements with that determined from solution measurements, and (6) other techniques for the rapid determination of orientation functions. Morphological information about uniaxially .deformed isotactic polypropylene films, obtained as a consequence of these developments, is reported. 1741 EXPERIMENTAL Preparation of FilmsCompression-Molded Unoriented Films. Profax 6523 was compressionmolded into 5-mil films at 550°F. for 10 min., cooled to 400"F., and treated in the following manner: ( I ) quenched in a Dry Ice-cellosolve bath (-65°C.); (2) quenched in tap water (20°C.); (3) placed in hot tap water (55°C.); (4) press cooled.Cast and Annealed Polypropylene Films. Profax 6320 was cast from the melt (ca. 280°C.) on a 20°C. roll at approximately 5 ft./min. The drawn films were produced by transferring cast film to a 110°C. roll and hot drawing over a 5-ft. gap to a room temperature roll. Sections of each of the films about 12 X 8 in. were annealed at fixed length for 15 min. at 110°C. and allowed to age for at least two months before being examined. DensityDensities were measured in a 3A alcohol-water density gradient coluinii at 23.2 f 0.1"C. X-Ray DiffractionX-ray diffraction measurements were made with a I'hilips diffractoineter equipped with a copper target, nickel filter, and a scintillation counter detector system. The measured intensities were corrected for polarization, absorption, background, and incoherent scattering. Calculations were made on a Bendix GlCiD computer. BirefringenceBoth birefringence and sonic velocity were measured on the %me strips of 1-5-mil film. These strips were 1 mm. wide and 15-25 cm. long. The thickness at each point examined was measured with a Pratt and Whitney Electro-Limit Gage. The retardation of the sample was measured in a Zeiss polarizing microscope with the use of a Zeiss interference filter to produce X = 546 mp monochromatic light. Both quartz and calcite Ehringhaus compensators were used to measure the retardation. S...