{'fraction_non_alphanumeric': 0.036290322580645164, 'fraction_numerical': 0.017857142857142856, 'mean_word_length': 5.010380622837371, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
COVID-19 vaccines and coronavirus 19 variants including alpha, delta,
 and omicron: present status and future directions

Coronavirus disease 2019 (COVID-19) is caused by a coronavirus, also called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It has caused urgent global health problems worldwide. The rapid spread of this pathogen, the development of its variants, and the escalating number of patients and their deaths prompted scientists to take up the race for immediate development of COVID-19 vaccines. With regard to the technologies available for vaccine development, mRNA-, inactivated virus-, viral vector-, and protein subunit-based vaccines have been developed thus far. This review article aimed to epitomize the current intelligence and improvements of various vaccines against COVID-19, explicitly those approved for urgent use. protein unites its host receptor, the dimeric human angiotensin-converting enzyme 2 (hACE2), through the RBD and detaches the S1 subunits. Breakage at S1–S2 and S2′ spots facilitates structural reorganization of the S2 subunit needed for virus–host cell membrane fusion. The S2-trimer in its post-fusion formation is depicted. The RBD is an interesting vaccine targeting point. The formations of an RBD-dimer or RBD-trimer have been reported to augment the immunogenicity of RBD-related vaccines. A balanced S-trimer presented with a C- terminal trimer-tag is a destined spot for vaccines. The pre-fusion S protein is a natural constant status during in vitro preparations and likely to convert into its post-fusion formation. Mutation of two residues (K986 and V987) to proline preserves S protein (S-2P) and hinders the pre-fusion to post-fusion systemic structural switch.